Chapter 3 – Prenatal Development and Birth
Parity: whether a woman has had a child before.
Perinatal factors: those occurring
Stages of prenatal Development
the ovum only last 3 to 5 days
prenatal dev. Is 38w, three trimesters: the zygote, the embryo and the fetus.
first tow weeks of life
sperm fertilizes the ovum, creates a zygote. The zygote goes down fallopian tube
and implants in the wall of the uterus (7 days in).
zygote has tendrils that penetrate the wall of the uterus (forms dependence)
The second trimester is where the embryo begins.
Beginning of the third week until the eighth week.
Crucial structurs form in mothers uterus: 1)The amniotic sac (membrane
containing watery fluid that protects organism from physical shocks, and temp.
changes. (2) the placeta: fleshy, disc like structure formed by cells from lining of
uterus and zygote. Works with umbilical cord. (3) umbilical cord:tube that
contains blood vessels, carries blood back and forth with the placenta. It carries
oxygen and nutrients and removed carbon dioxide and waste. Does not permit
direct blood exchange between mother and baby.
The membrane within the placenta is semi permeable which allows some
substances to pass through.
3 layers are created:
(1) ectoderm: hair, nails , parts of teeth, layer of skin and skin glands, sensory
cells and nervous system.
(2) Mesoderm: muscles, skeleton, circulatory, excretory and inner skin layer
(3) Endoderm: gastrointestinal tractm trachea, bronchia, Eustachian tubes, glands,
vital organs (lungs, pancreas and liver). th th
baby is very susceptible to envir. Assault. During this time (e.g. 4 and 5 week
the neural folds begin to close. If something prevents this closing the child will
end up with spina bifolda)
Prenatal dev. Is guided by 2 principles: 1) cephalocaudal: dev. From head to legs.
(2) Promimaldistal: internal organs and then distant areas.
By six weeks child looks like human, head is as large as the rest of the body
By the end of this period childs face, features, fingers, toes, external genetalia are
Miscarriage rates at this stage are high (1 in 4). The embryo becomes detached
from the wall of the uterus and is expelled through the vaginal canal. (some
women at this point don’t know they are even pregnan, nor do they realize they
had a miscarriage. A miscarriage can be beneficial because the baby had very little
chance of surviving. Most have chromosomal and genetic disorders. The Fetus
Fetus: organism is the third month to delivery.
Rapid growth in muscular dev. And the central nervous system.
End of the 4 month mothers normally report movement
Around 5 month reflexes appear (sucking, swallowing, and hiccupping).
After the 5 month fetus develops nails, sweat glands, coarser, more adultlike
skin, and soft hair that covers the body called lanugo, which they will normally
shth in the utero but some continue to shed it after birth.
6 month eyes can open and close
if infant is prematurely born at 6 months their regulatory processes, nervous and
respiratory systems usually aren’t mature enough for survival without intensive
intervention. At this point the fetus cant produce enough surfactant (a liquid that
allows the lungs to transmit oxygen from the air to the blood, which means they
cant breathe adequately and may develop respiratory distress syndrome (a
condition involving laboured breathing, grunting, flaring nostrils and bluish
discolouration of skin or mucous membranes.
At 22 to 26 weeks (age of viability: physical systems are well enough advanced
that it has a chance of survival if born prematurely). However, babies born before
28 weeks can have many difficulties especially with any added environmental
Risks In The Prenatal Environment
teratogen: and environmental agent (e.g. drug, medication, dietary imbalance,
polluting substance, that may cause structural or functional damage to in the
growing being. They are the most threatening during the embryotic period
however still capable of causing abnormalities in fetal stage.
1) A teratogen has a large effect on critical periods.
2) Each teratogen exerts specific effects. (e.g rubella affects fetus’s heart, eyes
3) A maternalor fetal genotype can counteract a teratogens effects. Their
genotypes determine if the baby will display any abnormalities.
4) The effects of one teratogen may intensify the effects of another. The moths
physiological status, nutrition, and hormonal balance can modify the impact of
a teratogen. (e.g. nutritional deficiencies: interfere with prenatal development
and also intensify adverse affects of drugs).
5) Different teratogen may produce the same defect. (e.g. deafness may be the
result from rubella or ingesting quinine of streptomycin).
6) The longer the fetus is exposed to the teratogen the greater the intensity and
more likely the fetus will be harmed. (e.g. the “doseresponse principle” the
higher the dose the more severe damage.
o Legal and Illegal drugs 90 percent of women take some sort of drug during pregnancy. Most of these
cases the woman don’t know they are pregnant yet. (e.g. 3 cups a coffee a day can
lead to miscarriage or low birth weight, asprin can lead to low birth weight, lower
iq, and poor motor control.
o Nicotine and Alcohol
in Canada and the us more than 30% of woman smoke while pregnant.
In the us 80% drink, whereas in Canada only 1725% drink.
Smoking and drinking leads to disturbances in placenta functioning, that lead to
oxygen deprivation, which leads to changes in the brain.
The rate for miscarriage, premature birth and low birth weight is higher
SIDS: infant 6 months or younger stop breathing and die without apparent cause.
Smoker babies are at higher risk of nicotine addiction in adolescence or
Prenatal nicotine exposure has significant cognitive effects as well. Ranging from
poorer performance in verbal comprehension, fine motor skills (13months),
poorer language dev., (34 years). visual and auditory attention (47 years),
visuoperceptual functioning (912 years), to intellectual, attention, memory, (in
Passive smoking (second hand). Can cause low birth weight, intellectual and
behavioural delays. Increased risk for illness (pneumonia, bronchitis, laryngitis,
otitis media and inner ear infection.
Alcoholic mothers: increased rate of dwarfism in England. 6% of mothers are
alcoholics, increasing their childs rate for fetal alcohol syndrome ( stunted
growth, number of physical and physiological abnormalities and often mental
Recently researchers introduced the term Fetal Alcohol Spectrum Disorder: it
describes any number of affects assisciated with exposiure to alcohol.
* It is not known how much or little alcohol comsumption leads to problems.
Fetal damage associated with acohol comsumption seems to be greatest in the last
trimester. Woman who cease drinking during that time may have babies with very
little abnormalities if any.
FASD babies: abnormal behaviours: irritable, distractible, hyperactive, rhythmic
rocking, banging heads.
Even moderate drinking can cause abnormal behaviours in children.
Higher risk of psychiatric disorders and alcohol problems.
Men that drink heavily can also lead to genetic damage of child.
Prevention: increase public awareness, televised advertisement, labels on
beverages, and warning signs put up where you can purchase. (some studies
indicate that they are helpful, some indicate they are only helpful in short term).
o Heroine, Cocaine, and Other Drugs babies become addicted and experience withdrawal symptoms (e.g irritability,
minimal ability to regulate state of arousal, trembling, shrill crying, rapid
respiration, and hyperactivity).
Often premature and low birth weight (makes it harder to cope with withdrawal
Can lead to infant death, unless mother stops in the third trimester.
They will need special care that they are less likely to receiv from drug using
parent. They don’t readily cling or cuddle. May disrupt parentchild relationship
Cocaine: not all parents have babies with dev. anomalies, cocaine is related to
physical defects (e.g. bone, genital, urinary tract, kidney, eye, heart deformaties,
brain hemorrhages). Some have problems with attention, distractible, and difficult
to control but it is very dependent on their environment. The effects are very
controversial. IQ scores were not lower, language development was.
Marijuana: mixed findings from studies. Some studies show cognitive impairment
in children whose mothers were heavy users, but is not evident until age 4.
Recently they did a study and saw no cognitive impairment.
o Environmental Toxins
Lead: premature, low birth weight, brain damage, physical defects, long term
cognitive and intellectual functioning.
Polychlorinated Biphenyls: banned mid 1970’s, common in electrical
transformers and capacitators. Contaminated fish gave birth to smaller, less
responsive, less neurologically advanced. Long term effects are lower IQ, poorer
memory, lower reading ability, higher levels of impulsivity in 411 yr olds. Inuit
infants are born with more PBC in their umbilical cords.
Men exposed to these harmful toxins can affect their sperm which can cause birth
Medical Interventions in Pregnancy and Childbirth
o Some therapeutic Disasters
In 1947 to 64 the synthetic hormone Diethylstilbestrol(DES) was prescribed to
prevent woman from miscarrying. Many female offspring developed vaginal
abnormalities and cancer of the cervix in adolescence. There was also
spontaneous abortion, premature deliveries, lowbirth weight babies. The baby
boys had damage to their reproductive tract (seminal fluid abnormalities). It is
still on the market but only for treatment of cancer, and other illnesses like aids or
1960: Thalidomide: anti anxiety and anti nausea for morning sickness. Effects:
deformed eyes, nose, ears;cleft palate; facial palsy; fusing fingers and toes;
dislocated hip joint and malformation of heart, digestive and genitourinary tracts
and phocomelia ( limbs are missing, feet an hands are attached to torso). There
were no adverse affects on parents, animal trials didn’t always produce offspring
with defects. Reserpine: may lead to respiratpry problems. Tetrecyclines may depress infant
skeletal growth. Anti convulsant drugs may result in development of clift lip and
palate as well as heart and skeletal defects. Even asprin in high doses can produce
blood disorders in babies.
o Medications Used in Labour and Delivery
Large amounts of obstetrical medication during labour had babies that were less
responsive, less smiling, more irritable, depressed, motoric disorganized and had
disruptive feeding responses. They also normally experiences impaired attention
and motor abilities for the first month , but disappeared after that. Its effects are
dependent on mothers health, babies genes, length of labour, size of baby.
o Age and Parity
Woman under 15 and over 35 are likely to have more complications during
delivery and pregnancy.
Chance of getting pregnant declines steadily after 27 and by 40 your chances are
Older mothers: increased health risks hypertension and diabetes. Higher chance of
Older fathers: become less fertile with age and higher risk of birth defects due to
decrease in quality of sperm.