Ch 4: Prenatal development

Period of the embryo

Prenatal development - The period from implantation, around the third week, through the eighth week of pregnancy, when the basic structures of the body begin to form.

Ectoderm

Embryonic development - The outer cell layer that develops into the nervous system, skin, and hair.

Mesoderm

Embryonic development - The middle cell layer that develops into the muscles, bones, and circulatory system.

Endoderm

Embryonic development - The inner cell layer that develops into the digestive system, lungs, urinary tract, and organs such as the pancreas and liver.

Neural tube

Embryonic development - The primitive spinal cord that develops from the ectoderm and becomes the central nervous system.

Embryonic development during the third and fourth weeks

Prenatal development - The neural tube begins forming during the third week. By the end of the fourth week, the heart has formed and begun beating, facial features begin forming, and arm and leg buds appear.

Embryonic development during the second month

Prenatal development - The embryo becomes more human in appearance, growing about 1 mm per day. The eyes, ears, skeleton, limbs, and brain develop rapidly, and the brain directs the first muscular contractions.

Indifferent gonad

Embryonic sexual development - The early genital structure that develops into testes in a male embryo when triggered by a gene on the Y chromosome, or ovaries in a female embryo without that signal.

Embryonic circulatory system

Prenatal development - By the second month, the circulatory system functions independently, with the liver and spleen producing blood cells instead of the yolk sac.

Period of the fetus

Prenatal development - The period from the ninth week of pregnancy until birth.

During this period, the fetus grows rapidly, organ systems mature and become interconnected, movement and sensory abilities develop, and individual characteristics begin to emerge.

Fetal development during the third month

Prenatal development - Organ systems continue growing and become interconnected. The fetus can kick, make fists, twist its body, swallow, digest nutrients, and urinate. Sexual differentiation progresses, and the sex can be detected by ultrasound by the end of the third month.

Testosterone

Fetal sexual development - The male sex hormone secreted by the testes that is responsible for the development of the penis and scrotum.

Second trimester

Prenatal development - The period from the thirteenth through the twenty-fourth weeks of pregnancy, when fetal growth, movement, sensory abilities, and coordination increase rapidly.

Fetal development during the fourth month

Prenatal development - The fetus develops a more human appearance, its skeleton hardens, its heartbeat can be heard with a stethoscope, and its movements become more coordinated.

Fetal development during the fifth and sixth months

Prenatal development - Nails harden, skin thickens, and eyebrows, eyelashes, and scalp hair appear. The fetus develops sucking, swallowing, and other coordinated movements, and its visual and auditory senses become functional.

Vernix

Fetal development - A white, cheesy substance that covers the fetus to protect the skin from chapping.

Lanugo

Fetal development - Fine hair covering the fetus’s body that helps vernix stick to the skin.

Fetal auditory abilities

Prenatal sensory development - By around the sixth month, the fetus can respond to sounds and may discriminate between different sounds, suggesting a rudimentary short-term memory system.

Third trimester

Prenatal development - The last three months of pregnancy, when organ systems mature rapidly in preparation for birth.

Age of viability

Prenatal development - A point between the 22nd and 28th prenatal weeks when survival outside the uterus is possible.

Fetal development during the seventh month

Prenatal development - The fetus weighs just over 1.8 kg and is about 40–43 cm long by the end of the month. Nervous system organization improves, but premature infants may need oxygen assistance because their lungs are immature.

Fetal development during the eighth and ninth months

Prenatal development - The fetus gains weight and body fat, which helps insulate the newborn from temperature changes. Activity slows and sleep increases, and the fetus commonly settles into a head-down position in preparation for birth.

Fetal position

Prenatal development - The curled-up posture the fetus commonly assumes near the end of pregnancy, often with its head down at the base of the uterus.

First stage of labour

Childbirth - The stage when uterine contractions become stronger, more frequent, and regular, helping dilate the cervix and position the fetus for birth.

Prenatal development stages vs. trimesters

Prenatal development - The stages of development of the organism do not correspond directly to the pregnant woman’s trimesters. The organism passes through the zygote and embryo stages during the first trimester and becomes a fetus at about eight weeks after conception.

Prenatal development stages

Prenatal development - The three stages are the zygote, embryo, and fetus.

• Zygote: Weeks 1–2; the one-celled zygote divides, becomes a blastocyst, and implants in the uterine wall.
• Embryo: Weeks 3–8; major body structures and organs begin forming.
• Fetus: Week 9 until birth; organs grow, become interconnected, and mature.

Teratogens

Environmental influences on prenatal development - External agents, such as viruses, drugs, chemicals, and radiation, that can harm a developing embryo or fetus.

Possible effects include physical deformities, delayed growth, blindness, brain damage, intellectual disabilities, and death.

Sensitive period

Teratogens - A period during which an organism is most susceptible to certain environmental influences; outside this period, the same environmental influences must be much stronger to produce comparable effects.

Teratogen exposure principles

Prenatal development - The effects of teratogens depend on:

• Timing: The greatest damage occurs while the affected body part or organ system is forming rapidly.
• Individual susceptibility: Genetic makeup and prenatal environment influence the degree of harm.
• Different causes: Different teratogens can cause the same defect.
• Multiple effects: One teratogen can cause several different defects.
• Dose and duration: Higher doses and longer exposure generally increase the risk of serious harm.
• Paternal exposure: Some teratogens can affect development through the father’s exposure.
• Postnatal environment: Later outcomes often depend partly on the environment after birth.
• Sleeper effects: Some harmful effects do not become apparent until later in life.

Anytime malformations

Teratogens - Birth defects that can be caused by exposure to teratogens at any point during the prenatal period.

Rubella (German measles)

Teratogen — maternal infectious disease - A disease that may have little effect on the mother but can cause serious birth defects in an unborn child exposed during the first three to four months of pregnancy.

Possible effects include blindness, deafness, heart abnormalities, intellectual disabilities, and an increased risk of psychotic disorders later in life.

Toxoplasmosis

Teratogen — maternal parasitic infection - A disease caused by a parasite found in raw or undercooked meat and cat feces.

• First-trimester exposure can cause severe eye and brain damage.
• Infection later in pregnancy can cause miscarriage.
• Prevention includes thoroughly cooking meat, washing utensils that contact raw meat, and avoiding cat feces.

Syphilis

Teratogen — sexually transmitted infection - A sexually transmitted infection that may cross the placenta during the middle and later stages of pregnancy, causing miscarriage or serious birth defects.

Genital herpes

Teratogen — sexually transmitted infection - A sexually transmitted infection that can infect infants during birth, causing blindness, brain damage, or death if not diagnosed and treated.

Acquired immune deficiency syndrome (AIDS)

Teratogen — maternal infection - A viral disease that can be transmitted from a mother to her fetus or newborn and weakens the body’s immune system, ultimately potentially causing death.

Thalidomide

Teratogen — medication - A mild tranquillizer that, when taken early in pregnancy, can produce malformations of the limbs, eyes, ears, and heart.

It can cause phocomelia, a structural abnormality in which all or parts of limbs are missing or the hands and feet are attached directly to the torso.

The type of defect depends on when the medication is taken during development.

Aspirin

Potential teratogen — medication - Heavy use during pregnancy has been linked to decreased fetal growth, poor motor control, and infant death, although some studies did not confirm these findings.

Ibuprofen

Potential teratogen — medication - Use during the third trimester has been associated with an increased risk of prolonged delivery and pulmonary hypertension in newborns.

Caffeine

Potential teratogen — stimulant - Heavy use, described in the text as more than four soft drinks or cups of coffee per day, has been linked in some studies to miscarriage and low birth weight.

Lithium

Teratogen — prescription medication - Antidepressant medication containing lithium can cause heart defects when taken during the first trimester and may influence prenatal speech perception.

Oral contraceptives

Potential teratogen — hormonal medication - Taking oral contraceptives without knowing that one is pregnant has been associated with a slightly increased risk of heart defects and other minor malformations.

Diethylstilbestrol (DES)

Teratogen — synthetic hormone - A synthetic hormone formerly prescribed to prevent miscarriage that can produce cervical cancer in adolescent female offspring and genital tract abnormalities in males.

• Daughters exposed before birth have an increased risk of reproductive-organ abnormalities, cervical cancer, miscarriage, and premature delivery.
• Some exposed sons have developed minor genital tract abnormalities, although they may remain fertile.

Fetal alcohol spectrum disorder (FASD)

Teratogen — alcohol - The full range of congenital problems commonly observed in the offspring of mothers who consumed alcohol during pregnancy.

Possible effects include physical growth delays and physical, behavioural, intellectual, and learning difficulties ranging from mild to severe.

FASD physical effects

Teratogen — prenatal alcohol exposure - Babies may be smaller and lighter than average and may have distinctive facial features, such as a thin upper lip, smooth philtrum, and short eyelid openings. However, most individuals with FASD do not have obvious distinguishing facial features.

FASD cognitive and learning effects

Teratogen — prenatal alcohol exposure - Alcohol-related brain damage can affect learning, memory, attention, language, social skills, motor skills, visual perception, reasoning, and judgment.

Children may struggle with reading, mathematics, time management, money management, working memory, executive functioning, and processing speed.

FASD behavioural effects

Teratogen — prenatal alcohol exposure - Children may have difficulty controlling behaviour, act impulsively, become frustrated easily, be distracted, struggle to understand consequences, and forget skills they previously appeared to have mastered.

FASD sensitive period

Teratogen — prenatal alcohol exposure - There is no well-defined sensitive period for FASD; drinking late in pregnancy can be just as risky as drinking soon after conception.

Paternal alcohol exposure

Teratogen — alcohol - Alcohol can affect the male reproductive system by reducing sperm motility and sperm count and increasing abnormally formed sperm. Research also suggests that babies whose fathers use alcohol may have lower birth weights.

Cigarette smoking during pregnancy

Teratogen — tobacco smoke - Smoking during pregnancy can restrict fetal growth and increase the risk of miscarriage, low birth weight, and death shortly after birth.

It is also associated with cleft lip, cleft palate, abnormal lung function, newborn hypertension, ectopic pregnancy, and sudden infant death syndrome (SIDS).

Nicotine and carbon monoxide

Teratogens — cigarette smoke - These substances enter the pregnant woman’s and fetus’s bloodstreams and impair placental functioning, especially the delivery of oxygen and nutrients. Fetal nicotine concentrations may be higher than those in the pregnant woman.

Passive smoking

Teratogen — second-hand tobacco smoke - Exposure to other people’s cigarette smoke, which can expose a pregnant woman to nicotine and carbon monoxide and interfere with fetal growth.

Newborns exposed to parental smoking may be smaller and may experience respiratory infections, cognitive difficulties, speech-processing deficits, and behavioural challenges.

Prenatal nicotine exposure and newborn autonomic activity

Teratogen — cigarette smoke - Newborns exposed to nicotine before birth have been found to have faster heart rates during quiet and active sleep than newborns whose mothers did not smoke during pregnancy.

Prenatal smoking and later development

Teratogen — cigarette smoke - Children exposed to smoking before birth or through continued parental smoking after birth may show poorer cognitive performance, speech-processing difficulties, behavioural challenges, and neural profiles resembling ADHD.

Cleft lip

Teratogen-related birth defect - A congenital disorder in which the upper lip has a vertical opening or groove.

Cleft palate

Teratogen-related birth defect - A congenital disorder in which the roof of the mouth does not close properly during embryonic development, resulting in an opening or groove in the roof of the mouth.

Pulmonary hypertension in newborns

Potential teratogen-related effect - High blood pressure in the blood vessels of the lungs; the text associates an increased risk with ibuprofen use during the third trimester.

Ectopic pregnancy

Pregnancy complication associated with smoking - A pregnancy in which the zygote implants outside the uterus, such as on the wall of a fallopian tube.

Sleeper effects

Prenatal development - Harmful effects of prenatal exposure that are not obvious at birth but become apparent later in life, potentially affecting psychological development.

Illicit drugs

Teratogen — illicit drugs - Substances used during pregnancy that can harm fetal development. Prenatal exposure may affect physical growth, brain development, and later behaviour and learning.

Cocaine

Teratogen — cocaine - Prenatal exposure is associated with low birth weight, premature delivery, slower growth, and changes in brain structure and function. Some reported developmental difficulties may also be influenced by social, environmental, and economic disadvantages.

Opioids

Teratogen — opioids - Maternal opioid addiction increases the risk of miscarriage, premature delivery, and newborn withdrawal symptoms. Symptoms can include vomiting, dehydration, convulsions, irritability, weak sucking, high-pitched crying, tremors, and sleep disturbances.

Neonatal withdrawal

Teratogen — opioids and other addictive drugs - Withdrawal symptoms experienced by newborns when they are no longer exposed to a drug they were exposed to before birth. Symptoms may last several months and can sometimes be severe or life-threatening.

Specialized caregiving

Prenatal drug exposure - Enriching and specialized caregiving may help children exposed to drugs before birth improve their development and compensate for early difficulties. Boys may be especially vulnerable to prenatal drug exposure.

Marijuana

Teratogen — marijuana - Prenatal exposure is associated with low birth weight, greater likelihood of neonatal intensive care, and abnormalities in brain development and connectivity. Research has also linked exposure to behavioural disturbances, poorer reading and spelling achievement, attention difficulties, anxiety, and depression.

Radiation

Teratogen — radiation - High levels of radiation during pregnancy can cause severe developmental abnormalities, intellectual disability, and fetal death. The exact amount needed to harm an embryo or fetus is uncertain.

Environmental chemicals and pollutants

Teratogen — chemicals and pollutants - Toxic substances in the environment can harm prenatal development and may cause physical abnormalities or intellectual disability. Examples include pesticides, lead, mercury, and other heavy metals.

Polychlorinated biphenyls (PCBs)

Teratogen — PCBs - Industrial chemicals that can harm fetal growth and neurological development, even at low exposure levels. Prenatal exposure has been associated with smaller newborns, reduced responsiveness, and later difficulties with memory, verbal reasoning, attention, reaction time, and spatial reasoning.

Paternal exposure to environmental toxins

Teratogen — paternal environmental exposure - A father's exposure to radiation, anesthetic gases, drugs, alcohol, or other toxins can damage sperm chromosomes or cause mutations, increasing the risk of miscarriage and genetic defects. Both parents should limit exposure to known reproductive toxins.

Maternal malnutrition

Maternal nutrition - Inadequate nutrition during pregnancy can restrict fetal growth and cause low birth weight, reduced brain development, and later cognitive difficulties. First-trimester malnutrition can disrupt spinal cord formation and increase miscarriage risk; third-trimester malnutrition can result in small-headed, underweight babies.

Protein-calorie intake

Maternal nutrition - Adequate protein and calorie intake is especially important for fetal brain development and healthy growth. Nutrition alone may not fully prevent later cognitive difficulties if the child's postnatal diet and environment remain inadequate.

Magnesium and zinc

Maternal nutrition - Small amounts of magnesium and zinc in the mother's diet help placental functioning and reduce the incidence of birth complications.

Iodine deficiency

Maternal nutrition - Insufficient iodine can cause congenital hypothyroidism, sometimes called cretinism, which can lead to irreversible intellectual disability.

Folate

Maternal nutrition - A B-complex vitamin that helps prevent defects of the central nervous system. Folate is found in foods such as fresh fruits, beans, liver, tuna, and green vegetables.

Folic acid

Maternal nutrition - The synthetic version of folate, commonly taken in supplements to help prevent neural tube defects. The text recommends 0.4 mg daily, but not more than 1.0 mg, when planning pregnancy or as soon as pregnancy is suspected.

Spina bifida

Neural tube defect - A bulging of the spinal cord through a gap in the spinal column. Adequate folate or folic acid helps reduce the risk.

Anencephaly

Neural tube defect - A birth defect in which the brain and neural tube fail to develop or develop incompletely and the skull does not close. Adequate folate or folic acid helps reduce the risk.

Excessive vitamin A

Teratogen — excessive vitamin A - Excessive vitamin A intake during pregnancy can cause cleft palate, heart malformations, and other serious birth defects.

Accutane

Teratogen — Accutane (a vitamin A derivative) - A powerful anti-acne drug that can cause malformations of the eyes, limbs, heart, and central nervous system when used during pregnancy.

Maternal emotional stress

Maternal emotional well-being - Prolonged and severe stress during pregnancy is associated with restricted fetal growth, premature delivery, low birth weight, and birth complications. Temporary stressful events generally have few, if any, harmful consequences.

Stress hormones

Maternal emotional well-being - Hormones released during maternal stress, such as adrenaline, may cross the placenta and affect fetal activity and development. Stress may also divert blood flow away from the fetus and reduce the supply of oxygen and nutrients.

Effects of prenatal maternal stress

Maternal emotional well-being - Prenatal stress is associated with infant irritability, irregular feeding and sleeping, and possible later risks involving ADHD symptoms, anxiety, behaviour, and cognitive development. Outcomes vary, and some research suggests moderate stress may support aspects of fetal maturation.

Social support during pregnancy

Maternal emotional well-being - A mother's ability to manage stress and access support from friends or others can influence whether stress contributes to pregnancy complications. Counselling and stress-management support may help reduce risks.

Maternal age

Maternal characteristics - The safest age range for pregnancy is generally about 20 to 35 years. Mothers younger than 16 and mothers older than 35 face increased risks of certain pregnancy and birth complications.

Pregnancy in adolescence

Maternal age - Teenage mothers, especially those younger than 16, have higher risks of premature delivery, low birth weight, and birth complications. These risks are partly associated with poverty, poor nutrition, stress, and limited access to early prenatal care.

Pregnancy after age 35

Maternal age - Older mothers face increased risks of miscarriage, stillbirth, very preterm birth, and chromosomal abnormalities. However, most healthy, well-nourished older women who receive adequate prenatal care have normal pregnancies and healthy babies.

Neonate

Prenatal development - A newborn infant from birth to approximately 1 month old.

Prevention of birth defects

Prenatal development - Prospective parents can reduce (“prevent) the risk of birth defects by limiting exposure to teratogens, maintaining adequate nutrition, managing stress, and obtaining appropriate prenatal care. More than 95% of newborns are described in the text as perfectly normal.

Active-child effect

Developmental themes - The developing organism actively influences its own development, even before birth. For example, the effects of a teratogen can vary depending on the fetus's genotype, so some fetuses may be severely affected while others experience fewer effects.