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Prenatal development
Pregnancy = 40 weeks
Conception:
● Ovulation and conception start 2 weeks after menstrual cycle
● Ovum period = conception
● Union of sperm (male gamete) and ovum (female gamete)
● Gamete: reproductive cell containing half the genetic material of the donor
○ After conception, gametes have all the genetic material required to make
a new organism
○ Explains why babies are not just clones of their parents
Zygote (And its Subsequent Cell Stages)
● Starting point of development
● Fertilized egg cell; starting point for development of the organism
● Cell begins dividing exponentially within 12 hours of fertilization, doubling roughly 2x
a day
● In just a few days, the small zygote is a cluster of cells
● After 4
th
day, it has divided so many times that it becomes arranged into a hollow
sphere with an inner cell mass
● If this call of cells becomes successfully implanted in the uterine lining (before the
end of the 2nd week), the inner cell mass becomes an embryo
Components:
Other cells become the support system, including:
● Amniotic sac: fluid filled membrane that surrounds and protects the developing
organism
● Placenta: temporary support organ with semipermeable membrane, allowing
exchange of materials between the mother and the fetus
○ how baby breathes, oxygen, exchange of nutrients
● Umbilical cord: how fetus and placenta are connected; "lifeline"
The placenta acts like 2 way exchange system between parent and fetus (antibodies to protect
in utero and out, oxygen, minerals)
● The mother's body eliminates all materials
● Waste products like CO2 and urea go from the fetus --> mother
● Oxygen, nutrients, minerals, and antibodies go from the mother --> fetus
Identical twins (monozygotic)
● Splitting in half of 1 zygote (same genes)
● Identical genetic material
● Whether they share placenta and/or amniotic sac depends on when the cell splits
(when the zygote divides). If this occurs:
○ Before implantation = separate sac and placenta
○ Right after implantation = shared placenta independent sacs
○ Late after implantation = shared placenta and sac
Fraternal (dizygotic)
● 2 separate eggs are released in the fallopian tube and fertilized by 2 separate
sperms to provide 2 separate zygotes that share half the same genetic material
Developmental Processes
● 4 developmental processes transform a zygote to an embryo, and an embryo to a
fetus. These are:
○ Mitosis (cell division)
○ Cell migration – cells move away from point of origin
○ Cell differentiation – cells specialize with different functions in the body
(embryonic can develop into any part), ex. Internal organs developing,
brain developing
○ Apoptosis – certain cells are meant to die to give rise to different
structures
Apoptosis – fetal hand plate
● Requires cell death in between the ridges of the hand plate for the fingers to
separate
Embryo (3rd-
th
week)
● Major systems and internal organs begin developing (but do not complete)
○ Heart limbs, sensory organs, brain
● Cephalocaudal development – organs near head develop first and earliest (head to
tail development) compared to those farther from the head
○ Head to tail development
○ ex. Babies have big heads, mature sensory system (smell and taste) -
upper portion has been developing first
● This is why infants have wonky motor movements – limbs have not developed as
much
● Exposure to toxins have a strong impact on head and neurological system because it
develops first (ex. Alcohol )
Embryo's Neural Tube Development
At 4
th
week – neural tube begins to develop into the brain and spinal cord
● Neural groove fuses together first at the centre and then outward in both directions
as if 2 zippers were being closed
● Can detect and discriminate flavours in amniotic fluid and they make faces
● Results in flavour preferences before birth
Mennella et al and taste:
● Pregnant women who planned to breastfeed were separated into 3 groups
st
group drank carrot juice during pregnancy and water during lactation
nd
group drank water during pregnancy and then carrot juice during lactation
rd
(control) group just drank water during pregnancy and lactation
After birth:
● They gave infants carrot cereal
● Infants who were exposed to carrot juice either way showed fewer negative faces
when consuming carrot juice
● Those with water during both time periods had higher negative faces
● Mothers perceived to enjoy the carrot cereal more than the water mothers
● For intake, carrot babies consumed more than water babies
● Therefore what's learned prenatally influences babies after they are born and their
preferences
● Small correlation
Smelling
● Later in prenatal development, they can "smell" by inhaling amniotic fluid through the
nose
● Amniotic fluid takes on the odor from what mom eats
Hearing
● Sound influences fetal environment and is a prevalent feature
● Stimulates brain development
● The fetus can differentiate between the mother's voice and music or mother's voice
and another voice
Evidence of Prenatal hearing –a study had pregnant moms read cat in the hat aloud for last 6
weeks of pregnancy
● Later newborns were fitted with pacifier headset (sucking influenced what was heard)
● Patterns that they sucked determined what book was read
● If they sucked a certain way another book would play
● Babies tended to suck in the pattern that enabled them to hear the tory they were
more familiar with – if you kept playing cat in the hat, they would get bored due to
habituation
● They learn from experiences inside womb
Habituation – a simple form of learning that involves:
● A decrease in response to repeated or continued stimulation – seen at 30 weeks'
gestation in visual and auditory stimuli
● Can test whether babies have preferences later on
● Repeated stimulus
● Baby cares less the more the stimulus is presented (less response)
Dishabituation
● Introduction of a new stimulus rekindles interest following habituation to a repeated
stimulus
● When a novel stimulus occurs, sucking rate increases again = dishabituation
● Introduction of new stimulus rekindles interest following habituation to a repeated
stimulus
● Lower response = higher memory
Hazards to Prenatal Development
Teratogens - any potentially harmful external agent that can cause damage during prenatal
development
● Not every fetus who is exposed will be affected in the same way
● Individual differences in genetic susceptibility
● Cumulative impact – being exposed to multiple can increase risk and can cause long
term
● Fetal programming: Early conditions can program longer term effects
○ Ex. Women who starved during pregnancy due to food shortages – their
kids showed higher rates of obesity or heart disease
○ Some impacts can stay hidden until later
○ Sleeper effect
○ Drug called DES (to prevent miscarriages) seemed safe – babies whose
mother consumed this drug were more likely to develop cancer (taken in
1940s-60s)
● Effects depend on when the teratogen was encountered during prenatal
development
● Zygote is not susceptible to external factors within first 2 weeks (placenta has not
started really working yet), not enough is developed even if the pregnancy is going to
be viable
○ Sensitive period: time during which a developing organism is most
sensitive to the effects of external factors
○ Early period when neurological system is starting to develop
○ Different systems = different periods
● Dark green denotes rapid development = when defects can come into play
● Lighter green = less chance that baby will be impacted
○ Sensitive period effects – serious effects only when taken after 4-6 weeks
after conception (when nausea starts but also when limbs develop)
Environmental Pollutants:
● Different forms of pollution act in combination
○ Toxic metals, synthetic hormones, microplastics, pesticides, herbicides
● Air and water pollution
○ Big impact on fetuses
○ Ex. Grassy Narrows and White Dog First Nation – dumping of mercury by
nearby mill for 8 years resulting in widespread mercury poisoning,
including pregnant individuals, children and continued contamination
● Lead (pipes, even painting walls in house can be risky, pint (old paint), historic lead
in gasoline
● Future research – impact of fetal development from Nano plastics
The Birth Experience
● About 38 weeks of conception --> fetuses aged 35-41 weeks are not unusual and
generally safe
● What induces labour?
○ Not entirely sure
○ Proteins secreted by fetal lungs are a suspect in some theories (signals to
mom that it is ready to come out)
○ Fetus and placenta likely play a role
● Labour begins --> cascade of hormones
○ Ex. Oxytocin causes contractions of uterine muscles
■ Synthetic oxytocin is used to induce labor contractions
● Ideally, the fetus comes out head-down
○ Breech = feet first or butt first, very dangerous, sometimes physically
pushing on moms belly can flip baby
For mom:
● Muscles contracting and stretching = pain
For baby:
● Squeezing but no pain
● Squeezing helps shift baby shift low in birth canal --> crowning
● Babies' heads are soft and head plates are not fused together, during birth they will
move and shift to make birth easier
● Reduces overall size of fetus' large head as plates of skill overlap during birth
● This is why babies are sometimes born with misshapen heads
● Squeezing and contraction releases hormones, helps to stimulate hormone
production in the fetus which releases stress hormones like oxytocin to withstand
oxygen deprivation
● The physical squeeze pushes out amniotic fluid out of lungs to support breathing,
allows baby to take its first breath
● Later in life – when bones fuse together, the soft spot on skull will go away
● Newborns that are laid flat on their heads can get flat skulls
Newborn infants
● Healthy baby will immediately interacts with environment
● Cannot see very well – sees fuzzy shapes, colors
● How they explore and what depends on their states of arousal
● Calm baby may response more to stimulation
● Fussy baby may not react well to stimulus
State of arousal:
For western babies, there are 6 distinct states:
● Quiet sleep – 8 hours
● Active sleep – 8 hours
● Drowsing – 1 hour
● Alert Awake – 2.5 hours
● Active Awake – 2.5 hours
● Crying – 2 hours
● Cultural and individual differences influence how long baby stays in each state
States of Arousal – Sleep:
● Sleep twice as much as adults
● Important to their development
● Total sleep time declines throughout childhood regularly and slower throughout rest
of life
● REM (rapid eye movement) sleep:
○ 50% of newborn sleep
○ Associated with dreaming
○ May allow infants to be more active – stimulates high brain activity
● Non REM sleep:
○ Heart rate is slow, breathing slower, resting state, body is relaxed
State of Arousal – Crying:
● Uses it to communicate with parents, purposeful and adaptive communication
● Infants cry to get attention of caregivers
○ To get attention, hungry, pain, over stimulated, lack of stimulation
● Peaks at 6-8 weeks, decreases around 3-4 months
● Consoling the crying baby:
○ Infant mortality rates are 2-3x higher in Nunavut and Northwest Territories
compared to Nova Scotira and British Columbia
Study Negative Outcomes
Multiple Risk Models
● Risks often co-occur and are cumulative:
○ More risk factors = worse potential outcomes
○ Affected domains include attachment, language development, well-being,
social development, etc.
○ Children growing up in poverty experience multiple risks over time –
casues risk for development
● Poverty is a developmental hazard – more likely to face multiple risks
○ Multiple risks are strongly related to lower SES (socio-economic status)
Structural Racism
● Behaviours and beliefs that harm specific racial and ethnic groups
● Can result in residential segregation, uneven access to healthcare, and higher rates
of incarceration
● Affects fetal and newborn health due to resource ability and standards of health for
POC
Infant Mortality Rates in the US
● Race, in addition to income and socioeconomic status, can be important and even
have a stronger correlation compared to income (esp for black families)
● Even though they make a lot of money, they have a high rick os infant mortality
● Regardless of maternal income, mortality rates for black infants remain notably
higher than those of Hispanic, Asian, and white infants
Developmental Resilience
● Developmental resilience = successful development despit multiple and seemingly
overwhemling developmental hazards
● Risks do not automatically lead to poor outcomes
● Children show resilience in the face of challenges
● Resilient children often have:
○ Factors contributing to resilience = social responsiveness to others,
intelligence, and a sense of being capable of achieving their goals
○ Responsive care and stability from at least 1 caregiver
Prenatal Development Hidden from view, the process of prenatal development has always been mysterious and fascinating, and beliefs about the origins of human life and development before birth are an important part of the lore and traditions of all societies. (Box 2. describes one set of cultural beliefs about the beginning of life that is quite unlike those of Western societies.) BOX 2.1 A CLOSER LOOK Beng Beginnings Few topics have generated more intense debate and dispute than the issue of when life begins—at the moment of conception, the moment of birth, or sometime in between. The irony is that few who engage in this debate recognize how complex the issue is or the degree to which societies throughout the world have different views on it. Consider, for example, the perspective of the Beng, a people in the Ivory Coast of West Africa. According to the Beng, every newborn is a reincarnation of an ancestor (Gottlieb, 2004). In the first weeks after birth, the ancestor’s spirit, its wru, is not fully committed to an earthly life and therefore maintains a double existence, travelling back and forth between the everyday world and wrugbe, or “spirit village.” (The term can be roughly translated as “afterlife,” but “before life” might be just as appropriate.) It is only after the umbilical stump has dropped off that the newborn is considered to have emerged from wrugbe and become a person. If the newborn dies before this point, there is no funeral, for the infant’s passing is perceived as a return to the wrugbe. These beliefs underlie many aspects of Beng parenting practices. One is the frequent application of an herbal mixture to the newborn’s umbilical stump to hasten its drying out and dropping off. In addition, there is the constant danger that the infant will become homesick for its life in wrugbe and decide to leave its earthly existence. To prevent this, parents try to make their babies comfortable and happy so they will want to stay in this life. Amongst the many recommended procedures is elaborately decorating the infant’s face and body to elicit positive attention from others. Sometimes diviners are consulted, especially if the baby seems to be unhappy; a common diagnosis for prolonged crying is that the baby wants a different name—the one from its previous life in wrugbe. So when does life begin for the Beng? Because each infant is a reincarnation of an ancestor, in one sense, an individual’s life begins well before birth. In another sense, however, life begins sometime after birth, when the wru commits to life and the individual is considered to have become a person. The parent of this Beng baby has spent considerable time painting the baby’s face in an elaborate pattern. She does this every day in an effort to make the baby attractive so other people will help keep the baby happy in this world. In the fourth century b.c.e., Aristotle posed a fundamental question that influenced Western thought for the next 15 centuries: Does prenatal life start with a fully formed individual, composed of a full set of tiny parts, or do the many parts of the human body develop in succession? Aristotle argued in favour of the latter, which he termed epigenesis—the emergence of new structures and functions during development (we will revisit this idea in Chapter 3 in its more modern form, epigenetics). Seeking support for his idea, he took what was then a very unorthodox step: he opened chicken eggs to observe organs in various stages of development. Conception Each of us originated as a single cell that resulted from the union of two highly specialized cells—a sperm and an egg. These gametes, or germ cells, are unique not only in their function but also in the fact that each one contains only half the genetic material found in other cells. Gametes are produced through meiosis, a form of cell division in which the eggs and sperm receive only one member from each of the 23 chromosome pairs contained in all other cells of the body. This reduction to 23 chromosomes in each gamete is necessary for reproduction because the union of egg and sperm must contain the normal amount of genetic material ( pairs of chromosomes). The process of reproduction starts with the launching of an egg (the largest cell in the human female body) from one of the ovaries into the adjoining fallopian tube (see Figure 2.1). As the egg moves through the tube towards the uterus, it emits a chemical substance that acts as a sort of beacon, a “come-hither” signal that attracts sperm towards it. If an act of sexual intercourse takes place near the time the egg is released, conception, the union of sperm and egg, is possible. In every ejaculation, as many as 500 million sperm are released. Each sperm, a streamlined vehicle for delivering genes to the egg, consists of little more than a pointed head packed full of genetic material (the 23 chromosomes) and a long tail that whips around to propel the sperm through the female reproductive system. FIGURE 2.1 Female reproductive system A simplified illustration of the female reproductive system, with a fetus developing in the uterus (womb). The umbilical cord runs from the fetus to the placenta, which is burrowed deeply into the wall of the uterus. The fetus is floating in amniotic fluid inside the amniotic sac.
To be a candidate for initiating conception, a sperm must travel for about 6 hours, journeying 15 to 18 centimetres upstream from the vagina up through the uterus to the egg-bearing fallopian tube. The rate of attrition on this journey is enormous: of the millions of sperm that enter the vagina, only about 200 ever get near the egg (see Figure 2.2). Many of the sperm get tangled up with other sperm milling about in the vagina; others wind up in the fallopian tube that does not currently harbour an egg. And a substantial portion of the sperm have serious genetic or other defects that prevent them from propelling themselves vigorously enough to reach and fertilize the egg. Thus, any sperm that do get to the egg are likely to be healthy and structurally sound, revealing a Darwinian-type “survival of the fittest” process operating during conception.
The chemical signal emitted from the egg provides location cues for the sperm as they approach. Fascinatingly, there is evidence that eggs may have preferences about which sperm they attract, though the basis for this genetic compatibility is currently unknown. This chemical conversation leads the “preferred” sperm to swim more directly towards the egg (Fitzpatrick et al., 2020). Thus, the egg is vying for the sperm that it considers optimal right up until the moment of conception. As soon as one sperm’s head penetrates the outer membrane of the egg, a
transplants, the pregnant parent’s immune system aids in the development of the placenta. These crucial materials then cross the placenta and enter the fetal blood system. Waste products (e.g., carbon dioxide and urea) from the fetus cross the placenta in the opposite direction and are removed from the pregnant parent’s bloodstream via normal excretory processes. The placental membrane also serves as a defensive barrier against a host of dangerous toxins and infectious agents that can inhabit the parent’s body but would be harmful or even fatal to the fetus. Unfortunately, being semipermeable, the placenta is not a perfect barrier, and, as you will see shortly, a variety of harmful elements can cross it and attack the fetus. These support system structures are illustrated in Figure 2.1. The amniotic sac is connected to the placenta via the umbilical cord, which is a tube containing the blood vessels that run to the fetus. An Illustrated Summary of Prenatal Development The course of prenatal development from the 4th week postconception on is illustrated in Figures 2.5 through 2.11, and significant milestones are highlighted in the accompanying text. Notice that earlier development takes place at a more rapid pace than later development and that the areas nearer the head develop earlier than those farther away (e.g., head before body, hands before feet)—a general tendency known as cephalocaudal development.
During the last 3 months of prenatal development, the fetus grows dramatically in size, essentially tripling its weight. It also develops a wide repertoire of behaviours and learns from its experiences, as described in the next section. Table 2.1 summarizes the major milestones in prenatal development.
Fetal Experience and Behaviour Is the womb a haven of peace and quiet? Although the uterus and the amniotic fluid buffer the fetus from the external world, the fetus still experiences an abundance of sensory stimulation and is capable of learning and developing behaviours. Studies of fetal behaviour reveal many results consistent with the themes laid out in Chapter 1. Prenatal experiences shape the developing fetus (nature and nurture). The fetus participates in, and contributes to, its own development: the formation of organs and muscles depends on fetal activity, and the fetus rehearses the behavioural repertoire it will need at birth (the active child). There is also evidence for both continuity and discontinuity. To give just one striking example, 32-week-old fetuses whose heart rates were generally slower and who moved less were more behaviourally inhibited at 10 years of age (DiPietro et al., 2018). Despite their very different environments (discontinuity), fetuses and children show surprising similarities (continuity). Movement From 5 or 6 weeks after conception, the fetus moves spontaneously. Indeed, fetuses move far more than we are aware of—just 16% of movements detected by ultrasound are perceived by the pregnant parent (Johnson, Jordan, & Paine, 1990)! One of the earliest distinct patterns of movement to emerge (at around 7 weeks) is, remarkably enough, hiccups. Although the reasons for prenatal hiccups are unknown, one theory posits that hiccups are a burping reflex, preparing the fetus for eventual nursing by removing air from the stomach to make more room for milk (Howes, 2012). Swallowing is another important reflex that helps to prepare the fetus for survival outside the womb. Fetuses swallow amniotic fluid, most of which is excreted back out into the amniotic sac. The tongue movements associated with swallowing promote the normal development of the palate. In addition, the passage of amniotic fluid through the body helps the digestive system mature properly. Another form of fetal movement anticipates breathing after birth. For breathing to occur, the respiratory system must be mature and functional. Beginning as early as 10 weeks after conception, the fetus promotes its respiratory readiness by exercising its lungs through “fetal breathing,” moving its chest wall in and out. No air is taken in, of course; rather, small amounts of amniotic fluid are pulled into the lungs and then expelled. Fetal breathing is initially infrequent and irregular but then increases in rate and stability. By the third trimester, fetuses “breathe” roughly once per second (Ulusar, Sanhal, & Mendilcioglu, 2017). Touch The fetus experiences tactile stimulation as a result of its own activity. Fetuses have been observed not only grasping their umbilical cords but also rubbing their face and sucking their thumbs. Indeed, the majority of fetal arm movements during the second half of pregnancy result in contact between their hand and mouth (Myowa-Yamakoshi & Takeshita, 2006), as the fetus in Figure 2.12 demonstrates. Remarkably, fetuses’ choice of thumb to suck predicts later handedness; fetuses who suck their right thumb are more likely to be right-handed adolescents, whereas fetuses who suck their left thumb are more likely to be left-handed adolescents (Hepper, Wells, & Lynch, 2005).
As the fetus grows larger, it bumps against the walls of the uterus increasingly often. By full term, fetal heart rate responds to the pregnant parent’s movements, suggesting that their vestibular systems—the sensory apparatus in the inner ear that provides information about movement and balance—is also functioning before birth (Cito et al., 2005; Lecanuet & Jacquet, 2002). Sight Although it is not totally dark inside the womb, the visual experience of the fetus is minimal. Nevertheless, fetuses can process visual information by the third trimester of pregnancy, and, much like newborn infants, fetuses have visual preferences. In one study, researchers used 4-D ultrasound to measure what third-trimester fetuses preferred to look at by projecting light patterns onto the abdomens of pregnant parents (see Figure 2.13; Reid et al., 2017). Fetuses preferred light displays that are top-heavy (resembling correctly oriented faces) over those that are bottom-heavy (resembling inverted faces). These data suggest that infants’ predispositions to look towards facelike stimuli may not require postnatal experience (though see Scheel et al., 2018, for an alternative view). We continue the discussion of face perception and preference in infants in Chapter 5, Box 5.1.
Taste The amniotic fluid contains a variety of flavours, and fetuses like some better than others. Indeed, the fetus has a sweet tooth. The first evidence of fetal taste preferences came from a study performed more than 60 years ago (described by Gandelman, 1992). A physician named DeSnoo (1937) devised an ingenious treatment for pregnant parents with excessive amounts of amniotic fluid. He injected saccharin into their amniotic fluid, hoping that the fetus would help their parent out by ingesting increased amounts of the sweetened fluid, thereby diminishing the excess. And, in fact, tests of the pregnant parent’s urine showed that the fetuses ingested more amniotic fluid when it had been sweetened, demonstrating that flavour preferences exist before birth. Additional evidence that fetuses are sensitive to flavours comes from 4-D ultrasound images of fetal facial expressions (Ustun et al., 2022). Pregnant parents in their third trimester ingested a capsule that was intensely flavoured with either carrot or kale. About 20 minutes later, the fetuses were imaged using 4-D ultrasound, and their facial movements were coded. The fetuses exposed to carrot showed facial expressions more associated with positive emotions (“laughter face”),
whereas the fetuses exposed to kale showed facial expressions more associated with negative emotions (“cry face”), as can be seen in Figure 2.14. Do these results tell us that carrots made fetuses happy while kale made fetuses sad? Probably not. But this study does suggest that fetuses can discriminate between these different flavours.
Smell Amniotic fluid takes on odours from what the pregnant parent has eaten. Obstetricians have long reported that during birth they can smell scents like curry and coffee in the amniotic fluid of parents who had recently consumed them. Smells can be transmitted through liquid, and amniotic fluid comes into contact with the fetus’s odour receptors through fetal breathing, providing fetuses with the opportunity for olfactory experience. Prenatal scent learning plays an important role in many species’ early developmental processes, demonstrating the principle of phylogenetic continuity: humans share many characteristics and developmental processes with nonhuman animals due to our shared evolutionary history. For example, during the birth process in rats, the nipples on the underside of the mother rat’s belly are smeared with amniotic fluid. The scent of the amniotic fluid is familiar to the rat pups from their time in the womb, and it lures the babies to the mother’s nipples for nursing. When the mother rat’s nipples are washed immediately after birth, newborn rats fail to attach to her nipples (Teicher & Blass, 1977). This classic finding clearly demonstrates that nurture begins prenatally: experiences before birth play an important role in postnatal developmental processes. And, as described later in this chapter, human infants similarly show preferences for flavours that they experienced through amniotic fluid as fetuses. Hearing The prenatal environment is surprisingly noisy. Fetuses float in a soundscape dominated by the pregnant parent’s heartbeat, blood flow, and breathing. From the fetuses’ vantage point, digestive sounds occur roughly 5 times per second (Parga et al., 2018)! The noise level in the uterus ranges from about 70–95 decibels (the range from a vacuum to a lawn mower). The pregnant parent’s voice is particularly prominent. We know that the fetus hears the pregnant parent because its heart rate changes when the parent starts speaking (Voegtline et al., 2013). During the third trimester, external noises elicit changes in fetal movements and heart rate as well. For instance, Canadian researchers showed that fetal heart rate increases when recordings of the pregnant parent’s voice is played near the abdomen (Lee & Kisilevsky, 2014). Similarly, changes in heart-rate patterns suggest that fetuses can distinguish between music and speech played near the pregnant parent’s abdomen (Granier-Deferre et al., 2011). The uterine auditory experience appears to be particularly well suited to early brain development. In a study by Webb and colleagues (2015), a group of hospitalized infants born preterm spent several hours each day listening to recordings of the pregnant parent’s uterine sounds (including voices and heartbeats). At 1 month of age, their brain development was compared to another group of preterm infants who were only exposed to regular hospital sounds. The preterm infants exposed to womb sounds had larger auditory cortexes than the control group, suggesting that the sounds that fetuses typically hear during gestation may facilitate brain development. Because sound is such a prevalent feature of the fetal environment, it plays a major role in prenatal learning, as we discuss next. Fetal Learning To this point, we have emphasized the impressive behavioural and sensory capabilities of the fetus. Even more impressive is the extent to which the fetus learns from its experiences in the last 3 months of pregnancy, after the central nervous system is adequately developed to support learning. In the example of fetal learning that opened this chapter, infants remembered specific prenatal auditory experiences that were presented via audio speakers adjacent to the pregnant parent’s abdomen, such as repetitions of a single nonsense word (Partanen, Kujala, Tervaniemi, & Huotilainen, 2013) or a melody like “Twinkle Twinkle Little Star” (Partanen, Kujala, Näätänen et al., 2013). More direct evidence for fetal learning comes from studies of habituation, one of the simplest forms of learning. Much like adults and children, fetuses grow bored if a stimulus is repeated over and over again. This process is called habituation: a decrease in response to repeated or continued stimulation (see Figure 2.15). Habituation provides evidence of learning and memory: the stimulus loses its novelty (and becomes boring) only if the stimulus is remembered from one presentation to the next. When a perceptible change in the stimulus occurs, it becomes interesting again—a process known as dishabituation. Fetuses as young as 30 weeks gestation show habituation to both visual and auditory stimuli, indicating that their central nervous systems are sufficiently developed for learning and short-term memory to occur (Matuz et al., 2012; Muenssinger et al., 2013).
Fetuses also learn from their extensive experience with the pregnant parent’s voice. To test this idea, Barbara Kisilevsky from Queens University and her colleagues (2003) tested term fetuses in one of two conditions. Half of the fetuses listened to a recording of the pregnant parent reading a poem, played through speakers placed on their parent’s abdomen. The other half listened to recordings of the same poem read by an unfamiliar female voice. Fetal heart rate increased in response to the pregnant parent’s voice but decreased in response to the unfamiliar voice. These findings suggest that fetuses recognized (and were aroused by) the sound of their own parent’s voice relative to a stranger’s voice. For this to be the case, fetuses must be learning and remembering the sound of their parent’s voice.
After birth, do newborns remember anything about their fetal experience? The answer is a resounding yes! They still prefer to listen to the birth parent’s voice rather than to the voice of another person (DeCasper & Fifer, 1980). Furthermore, newborns prefer to listen to a version of their birth parent’s voice that has been filtered to sound the way it did in the womb, rather than to another person’s filtered voice (Moon & Fifer, 1990; Spence & Freeman, 1996). Newborns prefer to listen to the language they heard in the womb over another language (Mehler et al., 1988; Moon, Cooper, & Fifer, 1993). Finally, newborns remember the sounds of specific stories heard in the womb (DeCasper & Spence, 1986). Figure 2.16 describes the technique these researchers used to study prenatal learning.
After birth, do newborns remember anything about their fetal experience? The answer is a resounding yes! They still prefer to listen to the birth parent’s voice rather than to the voice of another person (DeCasper & Fifer, 1980). Furthermore, newborns prefer to listen to a version of their birth parent’s voice that has been filtered to sound the way it did in the womb, rather than to another person’s filtered voice (Moon & Fifer, 1990; Spence & Freeman, 1996). Newborns prefer to listen to the language they heard in the womb over another language (Mehler et al., 1988; Moon, Cooper, & Fifer, 1993). Finally, newborns remember the sounds of specific stories heard in the womb (DeCasper & Spence, 1986). Figure 2.16 describes the technique these researchers used to study prenatal learning.
to 30% of people who have given birth, and which is especially likely for those with previous histories of depression (Brummelte & Galea, 2016). In Canada, around 4% of pregnant parents take antidepressant medication (Dandjinou, Sheehy, & Bérard, 2019). Evidence regarding whether or not these medications are harmful to the fetus is inconclusive (Lusskin et al., 2018), raising difficult questions for pregnant parents who are depressed. Should they choose a pharmaceutical intervention for their depression and risk negative outcomes from the medication? Or should they choose not to treat their mood disorder and risk negative outcomes from the depression itself? One potential solution to this issue is the use of non-pharmaceutical treatments for depression, which many pregnant parents say they would prefer (Dimidjian & Goodman, 2014). Behavioural interventions, including cognitive behaviour therapy and mindfulness-based cognitive therapy, hold promise as ways to treat perinatal depression without the use of medication (e.g., Dimidjian et al., 2017). Opioids Another issue of high concern is the use of prescription opioid medications (e.g., Vicodin, Percocet, oxycodone) and the related use of illicit opioids, such as heroin, methamphetamine, and street fentanyl. Because they are designed to mimic the effects of neurotransmitters, they have the potential to wreak havoc on the developing brain. Prescribed for pain management or used illegally, opioids can be highly damaging to fetuses, who can become addicted themselves. In 2019, 1.4% of pregnant parents in Canada reported opioid use during their pregnancy (Grywacheski et al., 2021). Neonatal abstinence syndrome (NAS) is a form of drug withdrawal seen when fetuses exposed to opioids in the womb are born. The increased prevalence in NAS has been dramatic: in Canada, the rate of NAS per 1000 birth hospitalizations increased from 2.01 in 2004–2005 to 5.12 in 2015–2016 (Lisonkov et al., 2019). Common effects of NAS include low birth weight, problems with breathing and feeding, and seizures. Treatment for these newborns often requires medications such as methadone or morphine to manage withdrawal symptoms. As we mentioned earlier, teratogens often occur in clusters. In the case of opioids, the copresence of other maternal drug use (e.g., antidepressants or cannabis) increases the likelihood that the newborn will have NAS (Sanlorenzo, Stark, & Patrick, 2018). Cannabis Cannabis is of particular interest to researchers because it is so frequently used by people of reproductive age in Canada, particularly following its legalization in Canada in 2018. In 2019–2020, 4.6% of pregnant parents reported using cannabis during pregnancy (Bayrampour & Asim, 2021). Data on the effects of cannabis on fetal development are inconclusive because many users of cannabis also smoke cigarettes and/or use alcohol, and the effects of each drug are difficult to tease apart; some studies suggest that the combination of cannabis and tobacco is particularly problematic (Ryan, Ammerman, & O’Connor, 2018). Prenatal exposure to cannabis is also associated with a range of problems involving attention, impulsivity, learning, and memory in older children. The effects of opioids and cannabis on fetal development can be devastating, but the two drugs that wreak the most widespread havoc on fetal development are cigarettes (nicotine) and alcohol, which we turn to next. Cigarette smoking Smoking a cigarette causes both the pregnant smoker and their fetus to get less oxygen. Indeed, the fetus makes fewer breathing movements while the pregnant parent is smoking, and the fetuses of smokers metabolize some of the cancer-causing agents contained in tobacco. Secondhand smoke has an indirect effect on fetal oxygen as well, through the pregnant parent’s intake of cigarette gases when someone is smoking nearby.
The main developmental consequences of smoking while pregnant are slowed fetal growth and low birth weight, both of which compromise the health of the newborn and contribute to an increased risk of miscarriage. In addition, smoking is linked to increased risk of sudden infant death syndrome (SIDS; discussed in Box 2.2) and a variety of other problems, including lower IQ, attention-deficit/hyperactivity disorder (see Box 9.3), and cancer. As with other teratogens, there is a dose–response relationship: greater smoking intensity (as measured in the number of cigarettes per day) predicts worse outcomes, including stillbirths (e.g., Marufu et al., 2015). And, as with other teratogens, timing matters: the effects of smoking are greatest early in gestation (e.g., Behnke et al., 2013). However, in spite of the well-documented and widely advertised negative effects of smoking on fetal development, 8.2% of pregnant parents in Canada in 2017 reported that they had smoked during their pregnancy (Government of Canada, 2020).
E-cigarettes (e-cigs) are becoming increasingly prevalent as an alternative to conventional cigarettes. Many expectant parents believe that vaping is healthier for their fetuses than cigarette smoking (Wagner, Camerota, & Propper, 2017). While e-cigs avoid some of the issues related to smoke exposure, the use of nicotine in any form is a risk factor for fetal development and can affect fetal cardiac, respiratory, and nervous systems. In addition, because e-cigs are largely unregulated, they range greatly in the amount of nicotine they contain, with some brands containing far more nicotine than cigarettes do (Jiang et al., 2018). Thus, the perception of the benefits of e-cigs relative to traditional cigarettes may lead expectant parents to overlook the risks. Alcohol Alcohol use during pregnancy is the leading cause of fetal brain injury and is generally considered to be the most preventable cause. Between 2018 and 2020, 1 in 10 pregnant parents in Canada reported consuming alcohol during their pregnancies (Popova et al., 2021). This rate is similar to the worldwide estimate of the average prevalence of alcohol use during pregnancy, but there are substantial cultural differences (Popova et al., 2017). Rates are highest in European countries (25% overall, with the highest rate in Ireland at 60%), and lowest in countries in the Middle East, where Saudi Arabia, Qatar, and Oman report rates of 0% (though it is worth noting that stigma may lead pregnant parents in some countries to underreport alcohol use). These data suggest that alcohol use during pregnancy reflects broader cultural views about the use of alcohol, especially by women. When a pregnant person drinks, the alcohol in their blood crosses the placenta into both the fetus’s bloodstream and the amniotic fluid. Thus, the fetus gets alcohol both directly—in its bloodstream—and indirectly, by drinking an amniotic-fluid cocktail. Concentrations of alcohol in the blood of the pregnant parent and fetus quickly equalize, but the fetus has less ability to metabolize and remove alcohol from its blood, so it remains in the fetus’s system longer. Prenatal exposure to alcohol can result in fetal alcohol spectrum disorder (FASD), which comprises a continuum of alcohol-related birth defects (Liu et al., 2023). One frequently observed symptom of FASD is a characteristic set of facial structures, like the eyes, nose, and lips shown in Figure 2.18. Other forms of FASD can include varying degrees of intellectual developmental disorder, attention challenges, and hyperactivity. The rates of FASD in Canada are much greater than previously suspected, with an estimated prevalence of between 2% and 3%, based on a study of 7- to 9-year-olds tested in the Greater Toronto Area (Popova et al., 2018).
Even moderate drinking during pregnancy (i.e., less than one drink per day) can have both short- and long-term negative effects on development. So can occasional drinking if it involves binge drinking (four drinks or more on a single occasion). In Canada, it is estimated
that 1% to 2% of pregnant people engaged in at least one incident of binge drinking during the previous month (Lange et al., 2017). The negative effects can include low birth weight, increased risk for ADHD, and delays in cognitive development and school achievement (e.g., Bandoli et al., 2019). Given the research to date, the Society of Obstetricians and Gynaecologists of Canada recommends that pregnant people avoid alcohol altogether. Environmental Pollutants The bodies and bloodstreams of most Americans (including those of childbearing age) contain a noxious mix of toxic metals, synthetic hormones, and various ingredients of plastics, pesticides, and herbicides that can be teratogenic (Moore, 2003). These substances often have significant negative effects on the fetus. For instance, the infants of Inuit parents, whose diets are high in arctic fish, are exposed to lead, mercury, and polychlorinated biphenyls (PCBs) both prenatally and postnatally. This type of exposure has been associated with later difficulties in attention, cognition, and neuromotor development (Boucher et al., 2012; Boucher et al., 2014; Després et al., 2005). Air pollution from the burning of fossil fuels is associated with low birth weight and neurotoxicity and disproportionately affects low-income populations, both in North America and around the world (Perera, 2016). Often, different forms of pollution act in combination. For example, China’s rapid industrialization has led to a dramatic increase in pollution-related negative effects on fetuses due to the unregulated burning of coal, water pollution, and pesticide use (e.g., Ren et al., 2011). While progress has been made in eradicating some pollutants in Canada, the situation in Grassy Narrows and White Dog First Nations provides clear evidence that environmental hazards continue to pose risks. In the 1970s, peoples from the Grassy Narrows and White Dog First Nations, who lived near Dryden, Ontario, began experiencing the same symptoms as the residents of Minamata, Japan, a coastal town in Japan that suffered a similar case of factory-related methylmercury poisoning (Takaoka et al., 2014). A chemical and pulp mill had been dumping mercury into the English–Wabigoon River system and poisoning the fish that were the First Nations’ main source of food and income. Four decades after the mill stopped dumping mercury into the river system, mercury levels in fish still exceed safe levels and people continue to develop the symptoms of Minamata disease, including numbness in the limbs, difficulty walking a straight line, vision and hearing impairments, headaches, and exhaustion. Furthermore, this elevated exposure has contributed to premature mortality of members of the Grassy Narrows community (Philibert, Fillion, & Mergler, 2020). Such incidents highlight the impact that decisions by individuals, groups, and local governments can have on environmental factors, which can in turn have significant and sometimes disastrous consequences on fetal and child development. And these issues are not easily remedied; in 2019, the Supreme Court of Canada ruled that the pulp mill company was responsible for cleaning the mercury-contaminated site. In 2020, the community reached an agreement with the federal government to build a clinic to support those suffering from mercury poisoning (CBC News, 2021).
New potential teratogens are still being discovered. Nanoplastics, tiny plastic particles that are ubiquitous in single-use packaging, were detected in human placenta for the first time in 2021 (Ragusa et al., 2021). This alarming development raises the spectre of wide-ranging impacts on health and development, particularly related to the developing endocrine system, as well as potentially damaging the placenta itself (e.g., Enyoh et al., 2023). Maternal Factors Because the pregnant parent provides the most immediate environment for the fetus, some of their characteristics can affect prenatal development. These characteristics include age, nutritional status, health, and stress level. Age The age of pregnant parents is related to pregnancy outcomes. Infants born to teenagers who are 15 years or younger are 3 to 4 times more likely to die before their 1st birthday than are those born to young adults between 23 and 29 (Phipps, Blume, & DeMonner, 2002). The rate of pregnancy for people between 15 and 19 years of age in Canada declined from 3.6% of all live births in 2011 to 1.3% in 2021 (Statistics Canada, 2022d), yet rates of teen pregnancy are still high elsewhere in the world. In 2021, 14% of girls/women worldwide gave birth before age 18, and pregnancy/birth-related conditions are the second-highest cause of death for girls/women aged 15–19 (UNICEF, 2022). These higher pregnancy and mortality rates may be related to social and cultural factors such as pressure to marry young, lack of access to contraceptives, and sexual violence (World Health Organization, 2023). Increasing age of the pregnant person is also cause for concern. In recent decades, many people in industrialized countries, including Canada, wait until their 30s or 40s to have children. The mean age of first birth in Canada has continued to climb from 27.8 years in 1991 to 31.4 years in 2021 (Statistics Canada, 2022d). Techniques to treat infertility have continued to improve, increasing the likelihood of conception for older parents. Like many other risk factors, there is a dose–response relationship, with risk of negative outcomes for both parent and fetus increasing with maternal age. For example, children born to older parents are at heightened risk for developmental disorders such as autism (Sandin et al., 2016). The causal pathways linking each parent to their infants’ developmental outcomes are likely different, since only the pregnant parent contributes to prenatal environments and birth circumstances (Lee & McGrath, 2015). The other parent’s contributions may lie more in mutations and other chromosomal abnormalities, as we will discuss in Chapter 3. Nutrition The fetus depends on the pregnant parent for all its nutritional requirements. An inadequate supply of specific nutrients can have dramatic consequences. For instance, pregnant parents who get too little folic acid (a form of B vitamin) are at high risk for having an infant with a neural tube defect such as spina bifida (see Figure 2.4). While prenatal vitamins are frequently used to address these concerns, many parents do not know they are pregnant during the crucial early periods of gestation. Many processed foods, such as breakfast cereals, are fortified with folic acid to support nutrition during the early weeks of pregnancy. Other foods are naturally high in folic acid, including citrus fruits and dark leafy greens such as spinach and broccoli. Because malnutrition is more common in low-income families, it often coincides with the host of other risk factors associated with poverty, making it difficult to isolate its effects on prenatal development. However, one unique study of development in extreme circumstances made it possible to assess certain effects of malnutrition independent of socioeconomic status (SES). As we discussed earlier, people of all income and education levels suffered severe famine in parts of the Netherlands during World War II. Children conceived during the Dutch Hunger Winter have been followed into adulthood. In late middle age, individuals who had experienced malnutrition as fetuses showed impaired performance on attentional tasks and had prematurely aged brains, compared with those who had not (de Rooij et al., 2010; Franke et al., 2018)
Disease Although most illnesses that occur during a pregnancy have no impact on the fetus, some do. For example, if contracted early in pregnancy, rubella (also called the 3-day measles) can have wide-ranging developmental effects, including deafness, blindness, and intellectual developmental disorders. The Society of Obstetricians and Gynaecologists of Canada recommends that people who do not have immunities against rubella be vaccinated before becoming pregnant. Sexually transmitted infections (STIs) are also quite hazardous to the
the fetal lungs mature, they secrete a protein that helps to initiate labour (Mendelson, Montalbano, & Gao, 2017). While some of the mechanisms underlying the onset of labour remain mysterious, what is clear is that the fetus itself plays a key role. A better understanding of how the fetus triggers labour will be highly informative in developing interventions to decrease the likelihood of preterm birth, a topic we will address later in this chapter. Uterine contractions and the fetus’s subsequent progress through the birth canal are extremely painful for the pregnant parent. During early labour, contractions cause the cervix to dilate—reaching 10 centimetres by the end of labour. As the muscles contract, the fetus is pushed through the uterus and towards the vagina. This stage can take a long time, averaging 6 hours for a first-time birth, based on data gathered in the United States, but often lasting far longer (Laughon et al., 2012). If the fetus has not already rotated into the normal head-down position, the birth is considered to be breech, as occurs in 3% to 4% of term pregnancies, and can be quite dangerous because the umbilical cord can become constricted around the baby’s body or neck (Gray & Shanahan, 2022). During delivery, the pregnant parent will often feel a tremendous urge to push. Crowning refers to the point at which the baby’s head appears. After the baby emerges from the vagina, the birth process concludes with the expulsion of the placenta and umbilical cord, usually soon after birth. A retained placenta can lead to serious bleeding after childbirth, so health-care workers ensure that the placenta is fully delivered. Perhaps reflecting the importance of the placenta in the childbirth process, many cultures have practices surrounding its use. For example, the Hmong people, an Indigenous group in China and Southeast Asia, consider the placenta to be the infant’s first and most important garment. Many Hmong people choose to bury the placenta at home so that when a person eventually dies, their soul can put it on as they travel to the spirit world (Helsel & Mochel, 2002). These traditional practices dovetail with the increased prevalence of placenta and umbilical cord blood banking in Western industrialized communities. Because these organs have a high proportion of stem cells, they can be stored for later use in disease treatment, with potentially lifesaving benefits. Extensive hormonal changes also follow delivery, as the parent’s body clears away placental hormones and reacts to the new baby. Progesterone and estrogen levels decrease rapidly, helping to facilitate the production of colostrum, which is the first milk generated after birth. Oxytocin—the bonding hormone—surges. Prolactin, the hormone that helps produce breast milk, also increases after birth. Is birth also painful for the newborn? Not particularly, as best we can tell. Compare how much pain you feel when you pinch and pull on a piece of skin on your forearm versus when you wrap your hand around your forearm and squeeze as tightly as you can. The stretching is painful, but the squeezing is not. The parent’s pain comes from the stretching of their tissues, but the baby experiences squeezing. The squeezing that the fetus experiences during birth serves several important functions. First, it temporarily reduces the overall size of the fetus’s disproportionately large head, allowing it to pass safely through the pelvic bones. This is possible because the skull is composed of separate plates that can overlap one another slightly during birth (see Figure 2.19). The squeezing of the fetus’s head during birth also stimulates the production of hormones that help the fetus withstand mild oxygen deprivation during birth and help regulate breathing after birth. The squeezing of the fetus’s body forces amniotic fluid out of the lungs, in preparation for the newborn’s first, crucial gasp of air.
Diversity of Childbirth Practices Although the biological aspects of birth are the same everywhere, childbirth practices vary enormously. All cultures pursue the dual goals of (1) safeguarding the survival and health of both parent and baby and (2) ensuring the social integration of the new person. Groups differ, however, regarding the relative importance they give to these goals. An expectant parent on the South Pacific island of Bali assumes that the expectant parent’s partner and other kin, along with any children they may already have, will all want to be present at the joyous occasion of the birth of a new child. Female relatives, as well as a midwife, actively help throughout the birth, which occurs in the home. Having already been present at many births, Balinese parents know what to expect from childbirth, even when it is their first child (Diener, 2000).
A very different scenario unfolds in twenty-first-century North America, where the person in labour usually withdraws almost totally from everyday life. In most cases, birth occurs in a hospital, typically attended by a small group of family or close friends. The birth is supervised by a variety of medical personnel, most of whom are strangers. Unlike their Balinese counterparts, first-time Canadian parents have probably never witnessed a birth, so they may not have very realistic expectations about the birth process. Also, unlike in most societies, pregnancies in Canada have a 31% chance of ending in surgical delivery by cesarean (also called C-section)—a rate that is high relative to other countries (Canadian Institutes of Health Information, n.d.). It should be noted, however, that the rate of cesarean deliveries worldwide has increased in recent years: 21% of all childbirths were cesarean deliveries in 2021, and researchers estimate that this number will rise to one-third of all births worldwide by 2030 (Betran et al., 2021).Cesarean deliveries are intended to assist in cases of birth complications, and indeed they have saved untold numbers of lives. However, there are other reasons for the high number of surgical deliveries, including a vastly increased rate of multiple births (discussed in the next section), scheduling convenience for the physician and/or the parents, parental obesity, prior cesarean deliveries (which may necessitate future cesarean deliveries), and physicians’ attempts to decrease risk of lawsuits concerning medical malpractice should problems arise from a vaginal birth (e.g., Yang et al., 2009). Indeed, one study found that amongst a sample of births in the United States by cesarean delivery, nearly half did not appear to have any pregnancy complications (Witt et al., 2015). The Balinese approach to childbirth emphasizes the social goal of immediately integrating the newborn into the family and community—hence the presence of many kin and friends to support the parent and baby. In contrast, the belief that childbirth is safer in a hospital setting outweighs the resulting social isolation of parent and baby. And indeed, while the rates of home births are increasing in the United States (1.4% of all births in 2021; Gregory, Osterman, & Valenzuela, 2022), they remain riskier than hospital births (Snowden et al., 2015). One study found that in the United States, infant mortality in hospital births attended by certified midwives was significantly lower than infant mortality in home births attended by certified midwives (Grünebaum et al., 2016). It is worth noting, however, that in Ontario, Canada, where home births are more common (20% of all births) and well integrated into the health-care system, the mortality rates for home and hospital births are equivalent, possibly because it is standard practice to transfer home-birthing parents to the hospital when complications arise (as was the case for 25% of home births in this Canadian sample; Hutton et al., 2015). The practices in both Canada and Bali have been changing to some degree. In Canada, the social dimensions of birth are increasingly recognized by doctors and hospitals, which often now employ certified midwives for expectant parents who prefer a less medicalized birth plan. As in Bali, various family members—sometimes even
including the parents’ other children—are encouraged to be present to support the labouring parent and to share a family experience. Another increasingly common practice is the use of doulas, individuals trained to provide emotional and physical comfort during labour and delivery. This shift has been accompanied by decreased use of delivery drugs, enhancing the pregnant parent’s participation in childbirth and ability to interact with the newborn, including engaging in activities such as skin-to-skin contact, which promotes stabilization of physiological processes in the transition from the womb to the outside world (e.g., Rutgers & Meyers, 2015). One approach to address birth and health inequities in Canada has included sustainable funding for access to Indigenous doulas or “birth helpers” to provide culturally appropriate and safe support to Indigenous peoples (Wodtke et al., 2022). In addition, many expectant parents attend childbirth education classes through their birth centre or health system, where they learn some of what their Balinese counterparts pick up through routine attendance at births. Social support is a key component of these programs; the pregnant parent’s partner, or some other supportive person, is trained to assist during the birth. Such childbirth programs are generally beneficial, and obstetricians routinely advise expectant parents to enroll in them. At the same time that these changes are occurring in Canada, Western medical practices are being increasingly adopted in societies like Bali, in an effort to improve newborn survival rates.
As another example of alternate birthing practices, let’s consider the Ju/’hoansi of rural Botswana and Namibia, who often give birth outdoors and alone despite the dangers posed by animal predators, including lions. This practice is deeply intertwined with spiritual and cultural beliefs that have endured for centuries and reflects a specific view of individual development that sees the birth experience as a key event in a person’s maturation (Biesele, 1997). Though extreme when viewed from other cultural perspectives, and dangerous from a modern medical standpoint, the birthing traditions of the Ju/’hoansi illustrate the complex ways that childbirth, amongst other aspects of child development, are linked to the greater social and cultural context. Finally, it is important to consider the impact of broader societal events on childbirth practices. For example, during the lockdown periods of the COVID-19 pandemic in 2020 and 2021, many hospital systems around the world did not allow partners or other family into the delivery room, leading pregnant parents to labour and give birth without the support of loved ones. One study of English parents who gave birth during the first year of the pandemic reported that nearly 50% of respondents rated their childbirth experience as predominantly negative (Aydin et al., 2022). This isolation from extended family and friends often continued after the new parents returned home, as they tried to minimize the risk of COVID-19 infection for their new infant. Other forms of societal upheaval, including war and natural disasters, also heighten the already heavy emotional and physical burden of childbirth. In spring 2022, as the Russian invasion of Ukraine began, it was widely reported that pregnant parents found themselves labouring and giving birth in makeshift wards in basement bomb shelters, creating an otherworldly juxtaposition of fear, joy, and pain (Kramer, 2022). These experiences mirror testimonials from pregnant parents and medical providers in Syria and other war-torn countries (e.g., Bashour, Kharouf, & DeJong, 2021). Increased understanding of both the physical and emotional aspects of childbirth will help researchers devise interventions to support parents in even the most challenging circumstances.
The Newborn Infant Healthy newborns begin interacting with their new environment right away, exploring and learning about newfound physical and social entities. Newborns’ exploration of this uncharted territory is very much influenced by their state of arousal. State of Arousal State refers to a continuum of arousal, ranging from deep sleep to intense activity. As you well know, your state dramatically affects your interaction with the environment—with what you notice, do, learn, and think about. It also affects the ability of others to interact with you. Figure 2.20 depicts the average amount of time in a 24-hour period that newborns typically spend in each of six states, ranging from quiet sleep to crying. Within this general pattern, however, there is a great deal of individual variation. To appreciate how these differences might affect parent–infant interactions, imagine yourself as the parent of a newborn who cries more than the average baby, sleeps little, and spends less time in the awake–alert state. Now imagine yourself with a baby who cries relatively little, sleeps well, and spends an above-average amount of time quietly attending to you and the rest of their environment (see Figure 2.21). Clearly, you would have many more opportunities for pleasurable interactions with the second newborn.
The two newborn states that are of particular concern to parents—sleeping and crying—have both been studied extensively. Sleep Two facts about sleep and its development are of particular importance. First, the average newborn sleeps twice as much as young adults do. Second, the pattern of two different sleep states—REM sleep and non-REM sleep—changes dramatically with age. Rapid eye movement (REM) sleep is an active sleep state associated with dreaming in adults; it is characterized by quick, jerky eye movements under closed lids, a distinctive pattern of brain activity, body movements, and irregular heart rate and breathing. Non-REM sleep, in contrast, is a quiet sleep state characterized by the absence of motor activity or eye movements and more regular, slow brain waves, breathing, and heart rate. REM sleep constitutes fully 50% of a newborn’s total sleep time. The proportion of REM sleep declines quite rapidly to only 20% by 3 or 4 years of age and remains low for the rest of life. Why do infants spend so much time in REM sleep? Some researchers believe that it helps develop the infant’s visual system. Because newborns spend so much time asleep, they do not have much opportunity to amass waking visual experience. The high level of internally generated brain activity that occurs during REM sleep may help to make up for the natural deprivation of visual stimulation, facilitating the early development of the visual system in both fetus and newborn. Another way in which REM sleep may be adaptive for neonates is that the natural jerking movements (called myoclonic twitching) that occur exclusively during REM sleep may give infants opportunities to build sensorimotor maps (Blumberg, 2015). These twitching movements are most frequent during early development and may help the infant with the difficult problem of linking motor patterns with the specific sensations that they evoke. Another distinctive feature of sleep in the newborn period is that neonates’ slumbering brains do not become disconnected from external stimulation to the same extent that the brains of older individuals do. This stimulation allows newborns to learn during sleep. In one study, infants were exposed to recordings of foreign vowel sounds while they slumbered in the newborn nursery. When tested in the morning, their brain activity revealed that they recognized the sounds they had heard while asleep (Cheour et al., 2002). Although newborns are likely to be awake during part of their parents’ normal sleep time, they gradually develop the more mature pattern of sleeping through the night. Nighttime awakenings typically diminish over the course of the first postnatal year. However, there is a subset of infants who continue to
