CH4 Prenatal Development, Birth, and Newborns' Readiness for Life
-prenatal development-development that occurs between moment of conception and birth
- Inside womb, three stages as well, but stages pass quickly as organism becomes a zygote, then embryo,
and finally fetus.
- transition from embryo to fetus occurs at 8 weeks,
- full month before pregnant woman enters second trimester of pregnancy often, before aware
she is pregnant.
-foundations for all of embryo's major organs formed
-rest of the prenatal period time of growth, developing function, and refinement of organs and
From Conception to Birth
-moment of conception, take approximately 266 days for zygote to become a fetus ready to be born.
-period of zygote (or germinal period), lasts from conception through implantation, when zygote becomes firmly
attached to wall of uterus
- 10 to 14 days
-period of the embryo, beginning of third week through end of eighth
-all major organs formed , heart begins to beat
-period of fetus, lasts from ninth week of pregnancy until child is born
The Period of the Zygote
-two cells and all resulting cells continue to divide, forming ball-shaped structure, blastocyst, contain 60 to 80 cells
w/in4 days of conception
-inner layer of blastocyst, embryonic disk, becomes embryo, whereas outer layer of cells develop into
tissues that protect and nourish embryo
-blastocyst approaches uterus 6 to 10 days after conception, small, burrlike tendrils emerge from outer surface
tapping mother's blood supply
-This is implantation
-" window of implantation" during which blastocyst must communicate (biologically) with uterine wall,
-takes about 48 hours , occurs 7 to 10 days after ovulation, entire process completing about 10 to
days after ovulation
-nearly three zygotes out of four, including most of abnormal ones, fail to survive initial phase of
Development of Support Systems
-blastocyst's outer layer rapidly forms four major support structures that protect and nourish
-One membrane, amnion, watertight sac fills w/ fluid from mother's tissues
-purposes of sac and its amniotic fluid : cushion against blows, regulate temperature, provide weightless
environment for embryo to move
-in watery environment is balloon-shaped yolk sac
- produces blood cells until embryo capable of producing its own.
-attached to third membrane, the chorion, surrounds amnion , eventually becomes lining of
-allantois, forms embryo's umbilical cord.
Purpose of the Placenta
-fed by blood vessels from mother and embryo, although hairlike villi act as barrier prevents these two bloodstreams
-barrier is semipermeable,
-umbilical cord transports carbon dioxide and metabolic wastes from embryo.
-waste products cross placental barrier, enter mother's bloodstream, eventually expelled The Period of the Embryo
-lasts from implantation (roughly third week) through eighth week of pregnancy.
-third week, embryonic disk rapidly differentiating into three cell layers.
-ectoderm, will become nervous system, skin, and hair.
-mesoderm, will become muscles, bones, and circulatory system
-endoderm, will become digestive system, lungs, urinary tract, and other vital organs
-portion of the ectoderm folds into neural tube
- becomes the brain and spinal cord
-end of fourth week, heart has formed and begun to beat.
-embryo about .6 cm but already 10 000 times size of zygote
The Second Month
-becomes much more human in appearance
-grows about 1 mm per day
-primitive tail appears, soon enclosed by protective tissue , becomes tip of backbone, the coccyx
-middle of fifth week, eyes have corneas and lenses
-seventh week, ears well formed, embryo has rudimentary skeleton.
-Limbs developing from body outward; upper arms appear first, followed by forearms, hands,
-seventh and eighth embryo's sexual development begins w/ appearance of genital ridge indifferent gonad.
-end of second month, embryo slightly more than 2.5 cm long and weighs less than 7.0 g.
Period of the Fetus
-seven months of pregnancy, or period of fetus
-all major organ systems begin to function and fetus begins to move, sense , behave
-individuality emerges as different fetuses develop unique characteristics, ex different patterns of
movement and different facial expressions.
The Third Month
-organ systems formed earlier continue growth , become interconnected
-coordination b/w nervous and muscular systems allow fetus to perform many interesting
-male testes secrete testosterone-male sex hormone responsible for development of a penis and scrotum
-end of third month, sex of a fetus detected by ultrasound
The Second Trimester: The Fourth through Sixth Months
-13th through 24th weeks of pregnancy; second trimester.
-16 weeks, fetus approximately 20 to 25 em long , weighs about 170 g.
-15 or 16 weeks through 24 or 25, simple movements of tongue, lips, pharynx, and larynx increase in
complexity and coordination
-Infants born prematurely may have difficulty breathing suckling ; exit womb early stage in
development of these skill ; haven't had enough time to practice
-fetus begins kicking may be strong enough to be felt by pregnant woman.
-end of 16th week, fetus assumed distinctly human appearance, although stands virtually no chance of
surviving outside womb
-fifth and sixth months, nails harden, skin thickens, and eyebrows, eyelashes, and scalp hair appear.
-20 weeks, sweat glands functioning, heartbeat often strong enough to be heard
-fetus now covered w/ white cheesy substance called vernix and fine layer of body hair lanugo
-Vernix protects skin against chapping exposure to amniotic fluid
-lanugo helps vernix stick to skin.
-end of sixth month, fetus's visual and auditory senses clearly functional.
- some ability to discriminate b/w sounds.
- ability may indicate presence of a rudimentary, short-term memory system
The Third Trimester: The Seventh through Ninth Months
-all organ systems mature rapidly, preparing fetus for birth
-22 and 28 weeks after conception (usually seventh month), fetuses reach age of viability- point which survival outside uterus is possible
-28- to 32-week-old begin to show better organized and predictable cycles of heart rate activity; gross
motor activity; and sleepiness/waking activity
-indicate developing nervous systems sufficiently well organized to allow survival should birth be
-many fetuses born require oxygen assistance
-pulmonary alveoli (air sacs) in lungs too immature to inflate and exchange oxygen for
carbon dioxide on their own
-end of seventh month, weighs just over 1.8 kg and about 40.0 to 43.0 em long.
- month later grown to 46.0 em and put on another 0.5 to 1.0 kg.
-comes from a padding of fat deposited beneath skin later helps to insulate newborn infant from
changes in temperature.
- most comfortable position likely head-down posture at base of uterus, w/ limbs curled up
-stages of development through developing organism passes do not correspond to trimester stages used to
describe pregnant woman's experience
-developing organism passes through all three stages of prenatal development in pregnant
woman's first trimester.
Environmental Influences on Prenatal Development
-teratogens external agents ex viruses, drugs, chemicals, radiation can harm developing embryo or fetus
-causing physical deformities, severely retarded growth, blindness, brain damage, and even death
-sensitive period during which organism quite susceptible to certain environmental influences; outside period, same
environmental influences must stronger to produce comparable effects.
- Olli Heinonen : concluded many birth defects found among children in sample were anytime malformations-
problems could have been caused by teratogens at any point during prenatal period
-Some disease agents capable of crossing placental barrier , doing much more damage to a developing embryo or
fetus than pregnant woman herself
-embryo or fetus has immature immune system cannot produce enough antibodies to combat infections
-rubella (German measles) disease has little effect on mother but may cause number of serious birth defects in
unborn children who exposed in first 3 to 4 months of pregnancy.
-1941 McAllister Gregg, noticed many mothers who had rubella (German measles) early in pregnancy
delivered babies who were blind -doctors began to notice pregnant rubella patients regularly bore children w/ variety of defects : blindness,
deafness , cardiac abnormalities, and mental retardation.
-most dangerous during first trimester.
-60 to 85 %of babies infected first 8 weeks of pregnancy will have birth defects, compared to 50 %infected
in third month ; 16 percent weeks 13 to 20
-clearly illustrates sensitive-period principle.
- eye and heart defects greatest in first 8 weeks; deafness in 6 through 13.
Other Infectious Diseases
-toxoplasmosis : by a parasite found in many animals.
-may acquire parasite eating undercooked meat or handling feces of family cat that has eaten infected
-produces only mild cold like symptoms in adults, can cause severe eye and brain damage if transmitted to
during first trimester,
-induce miscarriage if strikes later in pregnancy
Sexually Transmitted Diseases/Infections
-capable of producing serious birth defects or otherwise compromising developmental outcomes
-syphilis, genital herpes, acquired Immune deficiency syndrome (AIDS)- especially hazardous.
- syphilis : pregnant women who receive no treatment run risk of miscarrying or giving birth to child who has
serious eye, ear, bone, heart, or brain damage
- genital herpes : kills about 1/3 of all infected newborns , causes disabilities: blindness, brain damage, and other
neurological disorders in another 25 to 30 %
acquired immunedeficiency syndrome (AIDS):
- ways of catching
- 1) prenatally, through placenta;
(2) while giving birth, when potential exchange of blood child as umbilical cord separates from
-(3) after birth, passed through mother's milk during breast-feeding
- fewer than 25 percent of babies born to HIV-infected mothers infected themselves.
- more than half of all HIV-infected infants living beyond age 6, w/ fair percentage surviving into
- virtually all HIV-infected youngsters eventually die from complications of infection,
The Thalidomide Tragedy.
1960 mild tranquillizer, sold over counter, said to alleviate nausea and vomiting in morning
- Thousands who had used thalidomide during first two months of pregnancy gave birth to babies w/
severe birth defects.
- often badly deformed eyes, ears, noses, and hearts, many displayed phocomelia- structural abnormality in
which all or parts of limbs missing and feet or hands may be attached directly to torso, similar to flippers.
- waited until 40th day before using thalidomide, usually not affected
Other Common Drugs
- 60 % of pregnant women take at least one prescription or OTC drug.
- Heavy use of aspirin linked to fetal growth retardation, poor motor control, and even infant death
- use of ibuprofen in third trimester increases risk of a prolonged delivery and pulmonary hypertension in
- heavy use of caffeine (, more than four soft drinks/ cups of coffee per day) to miscarriage and low birth
- antidepressants containing lithium can produce heart defects taken in first trimester - oral contraceptives contain female sex hormones,
-if woman takes the pill w/ knowing she is pregnant, her unborn child faces slightly increase
risk of heart defects and other minor malformations
- serious long-term effects diethylstilbestrol (DES)- active ingredient of drug widely prescribed for prevention
of miscarriages b/w mid-1940s and 1965.
- 1971clearly established 17- to 21-year-old females whose mothers used DES at risk for developing
abnormalities of reproductive organs ex rare form of cervical cancer
- fewer than 1 in 1,000 DES daughters developed disease thus far
- DES daughters who become pregnant more likely to miscarry or deliver prematurely.
- no conclusive evidence prenatal exposure to DES causes cancer in sons,
-small number of men exposed to DES before birth developed minor genital trait
- affects development of fetus directly and indirectly by compromising function of placenta
- Fetal Alcohol Syndrome (FAS) : group of serious congenital problems commonly observed in offspring of
mothers who abuse alcohol during pregnancy.
- fetal alcohol effects (FAE) group of mild congenital problems sometimes observed in children of mothers who
drink sparingly to moderately during pregnancy.
- referred to as Alcohol Related Neurodevelopmental Disorder (ARND)
- neurobehavioural defects in absence of characteristic physical signs
- most noticeable characteristics of FAS defects : microcephaly (small head) , malformations of heart,
limbs, joints, and face
-likely to display excessive irritability, hyperactivity, seizures, and tremors.
-smaller and lighter than normal, physical growth lags to normal age-mates.
-score well below average in intelligence throughout childhood and adolescence, more than 90 % display
major adjustment problems
-How much can pregnant woman drink w/o harming baby?
-no safe amount of alcohol can be consumed during pregnancy
-drinking can affect male reproductive system, leading to reduced sperm motility, lower sperm count,
-newborns whose fathers use alcohol likely to have lower birth weights than newborns whose
fathers do not
-1996-1997, 21.3 percent of children under age of 3 had mothers reported smoking during pregnancy
-90.9 percent reported smoking in third trimester of pregnancy, when negative effect on fetal health is
-positive association b/w smoking during first trimester and cleft lip, with or without cleft palate
-abnormal lung function and hypertension in newborns of women who smoked during pregnancy
-smoking retards rate of fetal growth , increases risk of miscarriage or death shortly after birth in otherwise
normal infants ,
- leading contributor to growth retardation and low-birth-weight deliveries
-associated w/ higher incidences of ectopic pregnancies & sudden infant death syndrome
- affect regulation of autonomic activity in neonates.
-hearts of neonates exposed to nicotine in utero beat more rapidly than those not exposed to nicotine
-Fetal concentrations of nicotine may be much as 15 percent higher than those of smoking women
-Newborn infants of fathers who smoke likely to smaller than normal
- women become recipient of 2nd hand smoke
-12.5 % of infants born in downtown Toronto, 3 % born in suburban nurseries prenatal exposure to drugs such as
-brain tissue of human fetuses reveals marijuana use during pregnancy associated w/ changes in functioning of basal nucleus of amygdala,
- an area of brain involved in regulation of emotional behaviour
-changes prevalent in male fetuses, may indicate utero exposure to marijuana causes impairment of
emotional regulation, especially for boys
-compared to children not exposed in utero, 10-year-olds whose mothers smoked one or more joints per day during
first trimester exhibited poorer performance on achievement tests for reading and spelling.
-evaluations of classroom performance lower than those nonexposed peers.
- Second-trimester marijuana use assoc deficits in reading comprehension + underachievement.
-heroin, methadone, etc : do not appear to produce physical abnormalities,
-:more likely than nonusers to miscarry, deliver prematurely, or stillborns
- some infants exposed to opioid drugs) show normal developmental progress by age 2
-indifferent parenting +other social & environmental risk factors, may be most likely contributor to poor
-boys may be especially vulnerable to effects of maternal prenatal drug abuse
-Cocaine known to constrict blood vessels of both mother & fetus, elevating fetal blood pressure, hampering flow
of nutrients and oxygen across placenta
- crack and coke babies often miscarried or born prematurely
-often display tremors, sleep disturbances, sluggish inattention to environment, tendency to become
extremely irritable when aroused
-linked to developmental deficits: lower IQ scores , impaired visual-spatial abilities problems w/ skills
critical to language development-auditory attention ,comprehension and verbal expression
-prenatal and postnatal environment influence severity of cocaine-related developmental deficits
-maternal distress shown to contribute to poor fetal growth over and above contributions made by prenatal
exposure to cocaine
-unpleasant demeanour many cocaine babies display interferes w/ emotional bonding normally occurs b/w infants
-failed to establish secure emotional ties to primary caregivers in first year
-seem to derive less joy from learning than nonexposed infants do
-include chemicals in environment that pregnant woman cannot control , may not even be aware of.
-atomic blasts of 1945 in Japan , teratogenic effects of radiation
-Not one pregnant woman within 0.8 krn of explosions gave birth to live child.
-75 % pregnant women within 2 krn seriously handicapped children who soon died,
-no one knows exactly how much radiation takes to harm an embryo or fetus,
-routinely advised to avoid X-rays, particularly of pelvis and abdomen
Chemicals and Pollutants
- everyday potentially toxic substances : organic dyes , colouring agents, food additives, artificial sweeteners,
pesticides, and cosmetic products
- risks associated w/ large number of common chemical additives and treatments remain to be determined.
- pollutants in air and water.
- may be exposed to concentrations of lead, zinc, or mercury, or antimony discharged into air or water
- known to impair physical health and mental abilities of adults and children and have teratogenic effects
- PCBs (polychlorinated biphenyls), outlawed but once widely used in plastics and carbon paper
- low-level exposure to PCBs, resulting from mothers eating contaminated fish from Lake Michigan, make
newborns smaller on average , less responsive and neurologically mature than babies
- age 4, children still performed poorly on tests of short-term , memory and verbal reasoning ability,
- associated w/ difficulty maintaining attention & slower reaction times
- children least proficient at task those exposed to high levels of PCB in utero and through breast feeding
father's exposure to environmental toxins can affect children - prolonged exposure to radiation, anesthetic gases, and other toxic chemicals can damage father's
chromosomes, increasing likelihood of child being miscarried/ having genetic defects
1) environmental toxins can affect reproductive system of either parent
-(2) both mothers and fathers should limit exposure to substances to known teratogens.
The Mother's Diet
- pregnant women often advised to eat healthy, high-protein, high-calorie diet
-gain about 1.0 to 2.0 kg during first three months of pregnancy
-about 0.5 kg a week thereafter, total increase of about 11.0 to 14.0 kg
- Severe malnutrition, occurs during periods of famine, stunts prenatal growth and produces small, underweight
- first trimester, malnutrition disrupt formation of spinal cord and induce miscarriages.
- third trimester, likely to result in low-birth-weight babies w/ small heads who wont survive first year
- fewer brain cells and lower brain weights
- sometimes show cognitive deficits later in childhood.
- babies whose diets remain inadequate after birth often apathetic and quick to become irritated
- Canada, poor women at risk for poor nutrition
- nutritional supplement programs have established in some areas
- Montreal Diet Dispensary Program initiated 1960s to promote positive pregnancy outcomes
among socially disadvantaged urban women
- Adding small amounts of magnesium Improves functioning of placenta , reduces incidence of many birth
- fetus need iodine to ensure normal thyroid functioning.
- lack of iodine congenital hypothyroidism, sometimes known as cretinism, disorder leads to irreversible
- diets rich in folic acid, B-complex vitamin found in fr