Fetuses can detect and learn from a range of stimuli coming from both the outside world and inside the mother’s body & they are affected by these stimuli after birth.

Prenatal Development

When does life begin?

• Beng, people in West Africa, believe every newborn is a reincarnation of an ancestor.

  • This belief affects parenting, and leads Beng to believe that life begins sometime after birth when the wru, or spirit of the ancestor, commits to the new individual.

• Aristotle asked does prenatal life start with a full formed individual or do the many parts of the human body develop in succession?

  • Aristotle believed in epigenesis - the emergence of new structures and functions during development.

Conception

• Conception is equally likely in both male and female embryos.

  • We know due to reproductive technologies and prenatal genetic tests that there is almost exactly a 50-50 split between males and females, but female fetuses are less likely than male fetuses to survive early gestation.

• Male fetuses are more sensitive than females to harmful external agents, which affects their ability to thrive after birth, so males are more likely to die from sudden infant death syndrome and have attentional disorders and autism spectrum disorders.

• Societal and cultural forces also play a role as male offspring are more highly valued, so female offspring are either killed or aborted.

• New research is exploring impact of climate change on sex ratios, and shows that climate change may increase ratio of boys compared to girls, and stress-related teratogens as result of extreme weather events and consequences may negatively impact male fetuses. However, there is no evidence to support any definitive statements.

Development Process

1. Cell Division

   • Zygote divides into 2 parts each containing a full complement of genetic material.

   • Those 2 divide into 4, 4 into 8, 8 into 16…

   • The zygote becomes a newborn consisting of trillions of cells.

     Embryo - the developing organism from 3rd to 8th week of prenatal development

     Fetus - the developing organism from the 9th week to birth

     Mitosis - cell division that results in two identical cells

2. Cell migration

   • Newly formed cells move away from point of origin.

3. Cell differentiation

   • All of embryo’s initial cells - embryonic stem cells - can develop into any type of body cell.

   • After several cell divisions, they specialize (how it happens is unknown, but location definitely influences its future development).

4. Death

   • Cell suicide (apoptosis) - is genetically programmed cell death.

   • Formation of fingers is dependent on death of cells in between ridges in hand plate.

   • Death is preprogrammed for cells that disappear from hand plates.

Hormones have major influence through prenatal development.

• Sexual differentiation.

  • Androgens - class of hormones that include testosterone and lead to development of male genitalia.

  • If there are no androgens, female genitalia develops.

• Fetal growth

  • Steroids like glucocorticoids limit fetal growth and help fetal tissues mature.

• Toward the end of gestation, the fetus increases production of these hormones to mature key organs.

Early Development

• The 4th day after conception, cells arrange themselves into a hollow sphere with a bulge of cells called the inner cell mass on one side.

• The stage where twins originate:

  • Identical (monozygotic) twins - twins that result from splitting in half of zygote, resulting in each of 2 zygotes having exactly same set of genes.

  • Fraternal (dizygotic) twins - twins that result when 2 eggs happen to be released into fallopian tube at same time, only have half their genes in common.

• By the end of first week, the zygote embeds in uterine lining and becomes dependent on mother for sustenance.

  • Balls of cells start to differentiate

  • The inner cell mass becomes an embryo.

• The rest of cells become the amniotic sac and placenta that help the embryo to develop.

• The 2nd week, the embryo folds into 3 layers.

  • The top layer → nervous system (nails, teeth, inner ear, lens of eyes, outer surface of skin)

  • The middle layer → muscles, bones, circulatory system, inner layers of skin, other internal organs

  • The bottom layer → digestive system, lungs, urinary tract, glands

    • A few days after the embryo becomes 3 layers, a U-shaped groove forms and folds at the top of this groove fuse, creating neural tube which eventually becomes the brain and spinal cord.

• Amniotic sac: transparent, fluid-filled membrane that surrounds and protects fetus

• Placenta:

  • Supports organs for the fetus

  • Keeps the circulatory systems of the fetus and the mother seperate.

  • The semipermeable membrane permits exchange of some materials between them (oxygen and nutrients from mother to fetus, carbon dioxide and waste products from fetus to mother)

• Amniotic sac is connected to placenta via the umbilical cord, which is a tube containing blood vessels that run to the fetus.

An Illustrated Summary of Prenatal Development

• Cephalocaudal development - pattern of growth in which areas near head develop earlier than areas farther from head

• At 4 weeks, embryo is curved so head and the tail-like structure at the end are almost touching.

• The primitive heart is visible, and an arm bud can be seen.

• The 5.5 week old fetus, nose, mouth, and palate are beginning to differentiate.

• At 8.5 weeks, the fetus develops further

• At 9 weeks, the bulging forehead reflects extremely rapid brain growth.

  • The eyes and ears forming, all internal organs are present, sexual differentiation has started, ribs are visible, fingers and toes have emerged, and nails are growing.

• At 11 weeks, the heart has achieved basic adult structure, spine, ribs, major divisions of brain developing.

• During the last 5 months, external genitalia is mostly developed.

• At 18 weeks, the fetus is covered with fine hair, and greasy coating protects its skin from liquid.

• The baby can raise its eyebrows, wrinkle its forehead, move its mouth at this point.

  

• At 28 weeks, the brain and lungs are sufficiently developed .

• The eyes can open and move, esp. during REM

• The fetus reacts to variety of sounds

  

During last 3 month, the fetus grows dramatically in size (3x weight)

Recap: milestones in prenatal development

Fetal Experience and Behaviour

Movement

• 5-6 weeks after conception, the fetus moves spontaneously.

  • It hiccups because fetus may be removing air from stomach to make room for milk

• It also swallows amniotic fluid

  • This promotes normal development of palate, and helps the digestive system mature.

• Fetal breathing

  • The fetus moves its chest wall in and out.

  • Its breathing is infrequent and irregular, but gets steadier and more regular later.

    • By the 3rd trimester, they “breathe” about once a second

Touch

• The fetus grasps its umbilical cord, rubs its face, and sucks its thumbs

• It bumps against the walls of the uterus.

• It responds to maternal movements, suggesting sensory apparatus in inner ear that provides info about movement and balance works before birth.

Sight

• The fetus can process visual info by 3rd trimester.

• The fetus has visual preferences.

  • A study suggested that infants like to look toward face-like stimuli before being born.

Taste

• Amniotic fluid actually has many flavours, and fetuses have preferences.

• For example, some fetuses have a sweet tooth.

Smell

• The odors of amniotic fluid is based on what the mother has eaten.

• Smells can be transmitted through liquid, and the fetus can smell when amniotic fluid comes into contact with its odor receptors through fetal breathing.

• Prenatal scent learning is important in many species’ early development processes. It demonstrates the principle of phylogenetic continuity, which is the idea that because of our common evolutionary history, humans share many characteristics, behaviours, and developmental processes with non-human animals, especially mammals

• Ex. during the birth process in rats, the nipples of the mother rat’s belly are smeared with amniotic fluid. The pups are familiar with this while they were in the womb, so they are lured to the mom’s nipples for nursing. However, when the mother’s nipples are washed immediately after birth, they don’t come for nursing.

• This shows that prenatal experiences are important in post-natal development.

Hearing

• The womb is surprisingly very noisy because of mother’s heartbeat, blood flow, breathing, and digestive sounds. It is about 70-95 decibels.

• The heart rate changes when the mother starts speaking, so teh fetus can hear generally, and when its mother speaks.

• During the last trimester, external noises elicit changes in fetal movements and heart rate.

  • Changes in heart-rate patterns suggest fetuses can distinguish between music and speech near the mother’s abdomen.

• Uterine auditory experience is very good for early brain development, and because sound is so prevalent in the womb, it plays a major role in prenatal learning.

Fetal Learning

• Infants remember some things they heard while in the womb, like a singular word or a melody

• Fetuses grow bored if a stimulus is repeated over and over again (habituation)

  • This proves fetuses learn and have memory.

• Dishabituation happens when a new stimuli is introduced.

  • Dishabituation is the introduction of a new stimulus which rekindles interest following habituation to the repeated stimulus.

• Fetuses do remember things after birth, like preferring their mother’s voice over other voices. They also learn and prefer tastes and smells from the womb.

  • However, there likely is no benefit to prenatal education programs as the fetal brain is unlikely to be developed enough to grasp specific content.

Hazards to Prenatal Development

Teratogens

• Teratogens are external agents that can cause damage or death during prenatal development. Many only cause damage if present during a sensitive period.

• Teratogens often occur in combination.

  • ex. For families living in poverty, it is hard to separate the effects of poor maternal nutrition, exposure to pollution, inadequate prenatal care, and psychological stress.

• Fetal programming

  • Late effects of prenatal experience that program physiological set points that are important to adulthood physiology.

    • ex. In the case of inadequate prenatal nutrition, the fetus’s metabolism adjusts to the nutritional deficiency in womb and does not reset after birth, which can lead to obesity.

• The effects can vary according to individual differences, for example, genetics

• Some teratogens could be further complicated by sleeper effects, which are when the issues don’t show up until years later.

Drugs

• Many prescription and over-the-counter drugs are safe for pregnant woman, but some are not.

  • ex. Accutane is used for acne and can lead to severe birth defects or fetal death.

• Antidepressants

  • Evidence towards whether they’re harmful to fetuses or not is inconclusive.

  • Many women use behavioural interventions like cognitive behaviour therapy & mindfulness-based cognitive therapy instead of medication.

• Opiods

  • Opioids have the potential to hurt the developing brain.

  • They can even cause fetuses to become addicted themselves.

    • Neonatal abstinence syndrome (NAS) is drug withdrawal seen when fetuses are exposed to opioids in the womb after birth.

      • Effects: Low birth weight, problems with breathing and feeding, and seizures.

• Marijuana

  • Prenatal exposure to marijuana is associated with problems with attention, impulsivity, learning and memory in older children.

• Cigarette smoking

  • The fetus gets less oxygen and metabolizes some cancer-causing agents in tobacco when exposed to cigarette smoking in the womb.

  • Effects: slowed fetal growth, low birth weight, increased risk of sudden infant death syndrome (SIDS), lower IQ, hearing deficits, ADHD, and cancer.

    • SIDS is the sudden unexpected death of an infant less than 1 year of age that has no identifiable cause.

  • The greater the smoking intensity, the worse the outcomes, including stillbirths (timing also matters).

• Alcohol

  • Alcohol is the leading cause of fetal brain injury.

  • Alcohol in blood crosses placenta into fetus’s bloodstream and amniotic fluid.

    • The fetus gets alcohol both directly and indirectly.

  • The fetus has less ability to metabolize it, so it remains in system longer.

  • This can result in fetal alcohol spectrum disorder (FASD)

    • Effects: facial deformities, intellectual disabilities, attention problems, hyperactivity, low birth weight, increased risk for ADHD, delays in cognitive development & school achievement.

Environmental Pollutants

• Environmental pollutants are toxic metals, synthetic hormones, plastics, pesticides, herbicides that are in the bloodstreams of most Americans, and can hurt the fetus

  • ex. high levels of polychlorinated biphenyls in fish lead to babies with smaller heads.

  • ex. china’s rapid industrialization lead to pollution-related birth defects.

• Dose-response relationship: higher lead levels in the mother increases the risk of miscarriage, preterm birth, and low birth rate.

  • This disproportionately impacts poorer communities.

Maternal Factors

Age

• Infants born to girls 15 years or younger are 3-4x more likely to die before 1st birthday than those born to mothers 23-29 years old.

• Industrialized countries → women with college degrees wait until 30s and 40s to have children.

• Dose-response relationship: the risk of negative outcomes for the mother and the fetus increases with maternal age.

  • This leads to a heightened risk for developmental disorders such as autism spectrum disorder.

  • The father’s contributions lie in mutations and other chromosomal abnormalities.

Nutrition

• Malnutrition can lead to nutritionally deprived fetuses.

• This leads to prematurely aged brains, and impaired performance on attentional tasks.

Disease

• STIs can be harmful

  • ex. CMV (herpes) can damage fetus’s central nervous system and cause other serious defects like hearing loss.

  • Genital herpes can lead to blindness or even death.

  • HIV can be transmitted in the womb or during birth, or even through breast milk for example.

• Zika

  • Mosquito-borne viral infection.

  • It can make the baby’s head much smaller than expected.

  • It can lead to hearing, vision loss, and seizures.

Maternal Emotional State

• The maternal emotional state leads to an altered hormonal environment for the fetus which may lead to long-term changes in how children and and adults cope with stress.

• Pregnant women in less wealthy countries report greater levels of stress than those from wealthier countries.

• Postnatal maternal stress is a stronger predictor of later outcomes than prenatal maternal stress.

The Birth Experience

• After 38 weeks, contractions begin.

• The fetus is squeezed out.

  • This reduces the disproportionately large head.

  • It also stimulates the production of hormones that help the fetus withstand mild oxygen deprivation during birth.

Diversity of Childbirth Practices

• All cultures focus on (1) safeguarding the survival and health of mother and baby and (2) ensuring the social integration of the new person.

• Some cultures have all female relatives present at birth and some only have medical professionals (some at home, some at a hospital)

  • The ones with females present make mothers more prepared for their own births.

• The diverse range of birthing practices highlights the influence of sociocultural context, and these practices can have a direct impact on the newborn.

The Newborn Infant

State of Arousal

• State refers to the level of arousal and engagement in the environment, ranging from deep sleep to intense activity.

• State dramatically affects interaction with environment, and ability of others to interact with you.

• Infants are in 6 states: quiet sleep, active sleep, drowsing, alert awake, active awake, and crying.

Sleep

• Newborns sleeps 2 times as much as young adults.

• REM sleep - active sleep state characterized by quick, jerky eye movements under closed lids and associated with dreaming in adults (50% of total sleep time)

  • REM sleep decreases to only 20% by 3-4 years of age and remains low.

  • Infants spend a lot of time in this state because it helps make up for visual stimulation, and this helps them learn during sleep (ex. recognize sounds they hear while asleep)

• Non-REM sleep - a quiet or deep sleep state characterized by absence of motor activity or eye movements and more regular, slow brain waves, breathing, and heart rate

Crying

• Infants cry because of illness, pain, hunger and etc.

• It peaks around 6-8 weeks of age.

• It tends to decrease around 3-4 months of age.

• Soothing is to stop a baby from crying. Repetitive sensation helps.

• Swaddling is to wrap the baby tightly in cloths or blanket. This produces a high level of tactile simulation and warmth.

• Colic is excessive, inconsolable crying by young infant for no apparent reason.

Negative Outcomes at Birth

• Apgar score - method for evaluating health of newborn immediately following birth based on skin tone, pulse rate, facial response, arm and leg activity, and breathing.

  Infant Mortality

• Infant mortality refers to death during first year of birth.

  • In America, this is mostly due to poverty.

  • In less developed countries, it could be due to war, famine, or extreme poverty.

Low Birth Weight (LBW)

• LBW is when birth weight is less than 5.5 pounds.

• Many are premature (born at 35 weeks after conception or earlier) or small for gestational age.

• High levels of airborne pollution, smoking, alcohol and environmental pollutants, such as lead and mercury, lead to low birth weight.

  • LBW leads to a higher chance of developmental problems (ex. greater incidence of sensory impairments, poorer academic achievement, more behaviour problems).

• The lower the birth weight, the more likely it is for the infant to have persistent difficulties.

• For the majority of LBW children, the negative effects gradually diminish.

• To help children with low birth weight, parents are encouraged to have as much physical contact and social interaction with children. This results in improved behavioural outcomes, greater weight gain, higher IQs, to name a few positive outcomes.

Multiple-Risk Models

• A negative developmental outcome is more likely when multiple risk factors are involved.

• For example, English children growing up in families with four or more risk factors (including maritial distress, low SES, paternal criminality, and maternal disorder), reported a heightened incidence of psychiatric problems.

• The more risk factors, the worse the potential outcomes.

  • These risk effects impact aspects of child functioning, ranging from attachment to language development to well-being.

• Inadequate prenatal care, poor nutrition, illness, emotional stress, cigarette smoking, drug abuse, and exposure to environmental and occupational hazards are more likely to be experienced by a woman living below the poverty line than a middle-class woman (not just in America but in Japan too, showing a link between income and birth outcomes).

• Structural racism - behaviours and beliefs that harm specific racial and ethnic groups - can result in residential segregation, uneven access to health care and high rates of incarceration, which impacts fetal and newborn health.

  • As structual racism impacts minorities, improving hospitals in minority communities helps address pregnancy-related health disparities.

• Despite overwhelming developmental hazards, developmental resilience (successful development in spite of multiple and seemingly overwhelming developmental hazards) allows children to do well.