Download Prenatal Development and Birth

Developmental Psych handouts, Prenatal Devt and Birth
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Prenatal Development and Birth
(1) Germinal Period (conception to implantation, 8-14 days)
Zygote  blastocyst  embryonic disk, trophoblast
►6-10 days after conception, implants into uterine wall
►1 in 4 zygotes survive this phase
(2) Period of the embryo (start of 3rd week to end of 8th week)
► formation of major organs, heart starts to beat
trophoblast  amnion, yolk sac, chorion, allantois
placenta:
►barrier to prevent mother’s and embryo’s bloodstreams from mixing
►semi-permeable lets oxygen, carbon dioxide, salts, nutrients pass)
►connects to embryo via umbilical cord (carries oxygen, nutrients to embryo,
and removes metabolic waste from embryo)
After implantation:
►embryonic disk differentiates into 3 layers of cells
1) ectoderm (hair, skin, nails, oil & sweat glands, nervous system)
2) mesoderm (muscles, bones, connective tissue, circulatory & excretory systems)
3) endoderm (digestive tract, trachea, bronchi, lungs, pancreas, liver)
►after 4th week post-conception, heart is beating, embryo is 10000 times bigger than a zygote
►during 2nd month embryo grows 1/30th of an inch every day, brain develops quickly
►by end of 5ht week, skeleton and limbs are forming, eyes have developed
►by 8th-9th week, sexual development begins” genital ridge (i.e. the “indifferent gonad”)
(3) Period of the fetus (9th week til birth, about 7 months)
►major organs start to work
►by end of 3rd month, organs are refined, bones hardening, muscles developing, fetus starts to
move limbs, wiggle fingers
►in 2nd trimester (4th, 5th, 6th months) sin thickens, nails harden, eyelashes and hair develop
►by 6th month (25 weeks) auditory and visual systems are functional; fetus is 15 inches long,
weighs about 2 lbs
►22nd to 28th week: brain and respiratory system develop; fetus is “viable”
► in third trimester (7th, 8th, 9th months) gain weight (fat), respiratory system strengthens
►by middle of 9th month, fetus is so big that it rests head-down, limbs curled around body (fetal
position). Mother has uterine contractions to prepare for childbirth.
Environmental Influences on Prenatal Development
Maternal Characteristics:
►age: < 15, greater odds of stillborn fetus or later-dying baby; higher odds of dying in
childbirth
> 35, greater risk of fetal and neonatal deaths, spontaneous abortion
►more than 50% of pregnancies are not planned; an unhappy mother may secrete more
adrenaline and other hormones which can affect the fetus
►babies of stressed mothers are fussier, more active, more difficult to feed, to get to
sleep, etc. Genetic inheritance? Stress hormones in utero? Field (1985): mothers are
more punitive and controlling in child-rearing
Developmental Psych handouts, Prenatal Devt and Birth
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►Nutrition:
 mother should gain 25-30 lbs while pregnant
 malnourished mothers risk congenital defects, long labor, stillbirth, infant
mortality in 1st year
Teratogen: anything that can harm a developing embryo or fetus leading to deformities, retarded
growth, brain damage, or death.
►effects on a particular organ or system are worse when that structure is being formed
►genetic susceptibility
►one teratogens can cause many defects; a single defect can be caused by many
teratogens; increased exposure/dose means more serious harm
Critical Period: a segment of time in which an organ or system is most sensitive to effects of a
teratogens – when it is developing.
Defects of head, CNS
Heart
Other organs, body parts
 3rd to 5th week
 3rd to mid-6th week
 2nd month
►Maternal Diseases
 rubella in pregnancy: blindness, deafness, cardiac problems, mental retardation
- worse in 1st trimester (50-80% affected)
- still high in 2nd trimester (13%)
 syphilis: if untreated, miscarriage is likely, as well as ear, eye, bone, brain damage;
worse in middle and later pregnancy
 herpes (cytomegalovirus, or CMV): blindness, deafness, brain damage, death
- most common infectious cause of congenital deafness and mental
retardation
- genital herpes can cross the placental barrier or be transmitted during
childbirth; can lead to blindness, brain damage, 33% of infected neonates die
 AIDS (HIV infection): 25% of babies with infected mothers are infected. Can get the
virus 3 ways:
1) prenatally if virus passes placental barrier
2) during birth, if blood is exchanged as umbilical cord separates from placenta
3) after birth via mother’s milk
► Drugs
 Thalidomide: a mild tranquilizer prescribed to pregnant women in the 1960s to
alleviate morning sickness. Led to thousands of defective children, esp. when taken
during 2nd month
- deformities of the eyes, ears, nose, hearts, fusion of fingers/toes, phocomelia
(parts or entire limbs missing, feet/hands may attach directly to torso)
o 21st day: no ears
o 25th – 27th day: deformed/missing arms
o 28th – 36th day: deformed or missing legs
o after 40th day: no effect
 caffeine: possibly miscarriage, low birth weight, poor motor control
 oral contraceptives: heart defects
Developmental Psych handouts, Prenatal Devt and Birth
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 Diethylstilbestrol (DES): ingredient in a drug used in the 1940s-1960s to prevent
miscarriage
- DES daughters are at risk for abnormalities of reproductive organs, cervical
cancer, miscarriage, early delivery
- DES sons are at risk for fertility, immune system problems
 alcohol:
- fetal alcohol syndrome (FAS): microcephaly, heart/limb/joint/facial
malformation, irritability, hyperactivity, seizures, small size, delayed physical
maturation, low IQ, mental retardation
- even moderate consumption (1-3 ounces per day) can lead to fetal alcohol
effects (FAE): retarded growth, motor skills problems, physical abnormalities,
poor attention span, subnormal IQ
 nicotine: retards rate of fetal growth, increases risk of spontaneous abortion, neonatal
death, impairs functioning of placenta
- Lefkowitz (1981): long term effects of maternal smoking on 9-11 year olds.
Found no differences in size, intelligence, behaviour, popularity.
 hallucinogens:
- heavy marijuana use linked to premature birth, low birth weight
- LSD  increased risk of miscarriage, stillbirth, chromosomal abnormalities in
offspring
 narcotics (codeine, heroin, morphine): miscarriage, premature delivery, stillborn
- 70-90& of babies born to heroin users are addicted at birth
► Environmental Hazards
 radiation: mutations, mental retardation, infant death, fetal death
 zinc, lead, mercury: impaired health and mental abilities, teratogenic effects on fetuses
 PCBs: smaller, less responsive neonates with long-term memory problems
Perinatal Environment: the environment surrounding birth (drugs given during labor and
delivery; practices used in delivery; environment after baby is born)
3 stages of childbirth
1st stage (8-14 hours for first-borns, 3-8 hours for later borns): contractions of uterus 10-15
minutes apart, leading to fully dilated cervix
2nd stage (1/2 hour to 1 ½ hours): starts when fetus’ head is at cervical opening
- head eventually passes through cervix into vagina
- eventually emerges from mother’s body
3rd stage, the afterbirth (5-10 minutes): placenta is expelled from uterus
Developmental Psych handouts, Prenatal Devt and Birth
Perinatal Hazards:
► Apgar test assesses 5 characteristics:
1. heart rate (0=absent; 1=slow; 2=over 100 beats/minute)
2. respiration (0=absent; 1=slow; 2=good, crying)
3. muscle tone (0=flaccid;1=weak, some flexion; 2=strong, active)
4. colour (0=blue, pale; 1=pink body, blue extremities; 2= completely pink)
5. reflexes (0=no response; 1=frown, grimace, weak cry; 2=vigorous cry, cough,
sneeze)
poor Apgar scores:
►anoxia (oxygen deprivation)
►positioning of fetus (1 in 10 are breach births, i.e. feet or bottom first; 1 in 500 breach
birth babies die at birth or soon after; 2 -4% have cranial bleeding or cerebral palsy)
►forceps can cause cranial bleeding, brain damage
►obstetric medication; up to 9% of mothers are on a drug while giving birth (analgesics,
sedatives, stimulants)
Brackbill (1985): babies of mothers who were medicated smile less, are irritable/inattentive, hard
to comfort or feed
Low birth weight:
► preterm infants
►small-for-date infants - more at risk for serious complications
Due to mothers’ smoking, drinking, poor nutrition; mothers who are too young; multiple births
Short term consequences:
► more than 50% of babies < 1000 grams (2.2 lbs) die at birth or shortly after
►malformations, malnourishment, genetic abnormalities
►respiratory problems due to lack of surfactin (coating on lungs)
Long term consequences:
► if in good homes, usually do fine
►if in disadvantaged/ unstable homes, likely to be smaller than other kids, more
emotional problems, long-term intellectual deficits
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