Chapter 4: Prenatal Development, Birth, and Newborns'
Readiness for life
Just b/c risk is associated with a certain behviaor does not mean that
engaging in the bhevaior will ensure that outcome. All sexuality active men
and women should be aware of the possibility of a preganancy, the critical
period of early weeks of pregnancy, and the wisdom of adjusting their
lifestyles to provide a healthy prenatal environment.
From conception to birth
From moment of conception, it will take around 266 days for the one-celled
zygote to go through 3 major phases, andbecome foetus of some 200 billion
cells ready to be born.
The period of the Zygote (1st phase)
From conception through implantations when the zygote becomes attached
to uterus lining and lasts about 10-14 days. As it moves down the fallopian
tubes, it undergoes mitosis into 2 cells, then a blastocyst that will contain 60
to 80 cells within 4 days of conception. Its inner layer will become the
embryo, while the outer layer will develop into tissues that protect and
nourish the embryo
• Implantation: occurs when a blastocysts approaches the uterus and
attaches in uterine wall. There is a specific window of implantation
during which the blastocyst must communicate biologically with the
uterine wall, position itself, attach and invade. It occurs about 7 to 10
days after ovulation and lasts about 48 hours. Only about half of all
fertilized ova are firmly implanted, and all others are either genetically
abnormal and fail to develop, or burrow into a site incapable of
sustaining them and are miscarried. Nearly 3 zygote out of 4 fail to
survive the initial phase.
• Development of Support sytems: Outer layer of blastocyst rapidly
forms 4 major structures to protect and nourish the developping
(1) amnion: watertight sac that fills with fluid from the mother's
tissues. this sac and the amniotic fluid cushion the developping
organism against blows, regulate its temperature, and provde
weightless environment that will make it easier for embryo to move.
Floting in this environment is a ballon shaped yolk-sac .
(2) yolk-sac: that produces blood cells until embryo is capable of
producing its own and is attached to 3rd membrane.
(3)Chorion: surrounds the amnion and will become linig of placenta (4) Allantois: form the embryo's umbilical cord.
• Purpose of Placenta: placenta is fed by blood vessels from the mother
and the embryo. Acts as barrier preventing both bloods to mix. Is
semipermeable allowing only certain substances to pass such as gases
(Oxygen), salts, and nutrients AND delivers it to the embryo. It also
transports metabolic wastes and carbon monoxide from embryo. PLays
a crucial role in prenatal development
The period of the embryo (2nd phase)
From beginning of 3rd week through end of 8th week. Period where all major
organs are formed and the heart starts beating. By 3rd week: embryonic disk
is rapidly differentiating into 3 cell layers: (1) Ectoderm (outer layer) will
become nervous system, skin and hair. A portion of it will fold into a neural
tube that will become brain and spinal cord. (2) Mesoderm (middle layer) will
become muscles, bones and circulatory system (3) Endoderm (inner layer)
will become digestive system, lungs, urinary tract, and other vital organs
such as pancreas and liver. By end of 4th week, heart has started to beat.
Embryo is about 0.6cm.
• The second month: embryo becomes more human in appearance as it
grows 1mm per day. A primitive tail grows and will become the coccyx.
By middle of 5th week, the eyes have corneas and lenses. By 7th
week, ears are well formed and embryo has rudimentary skeleton.
Limbs are developing from body outward; upper arms appear, then
forearms, hands and fingers. Brain develops rapidly during second
month as it directs organism's frist muscular contractions by the end of
embryonic period. During 7th-8th week, embryo's sexual development
beings with appearance of genital ridge called indifferent gonad. If it is
a male, a gene on Y chromosome will trigger a biochemical reaction
that instructs the indifferent gonad to produce testes. If it is a female,
then X chromosome will trigger the production of ovaries. Embryo's
circulatory system functions on its own. Embryo is slightly more than
2.5 cm long and weight less than 7.0 g.
The period of the fetus (3rd phase)
From 9th week of pregnancy until the baby is born. All major organs begin to
function, and developing organisms grows rapidly. Fetus begins to move,
sense and behave. Individuality emerges as different fetuses develop unique
characteristics such as different patterns of movement and different facial
• The third month: Organ systems that were formed earlie continue their
rapid growth and become interconnected. Coordination between
nervous system and muscular systems allow the fetus to perform many interesting manoeuvres (ie. kicking its legs) but still too subtle to
be felt by pregnant woman. The digestive and excretory systems are
also working together. Sexual differentiation is rapidly progressing.
Male testes secrete testosterone and develop penis and scrotum. In
absence of it, female genitalia form. By end of 3rd month, sex of fetus
can be detected by ultrasound and its reproductive system already
contrains immature ova or sperm cells. Already there after 12 weeks
when fetus is 7.5cm and weights less than 28g.
• The second Trimester: the fourth through sixth months: Development
occurs at rapid pace during 13th through 24th weeks of pregnancy. At
16 weeks, fetus is about 20-25cm long and weight about 170g. From
15-25 weeks, simple movements of the tongue, lips, pharynx, and
larynx increase in complexity and coordination, so fetus begins to suck,
swallow, munch, hiccup, coudh and snort; preparing for extra-uterine
life. Fetus begins to kick strong enough to be felt by pregnant woman.
Fetal heartbeat can be easily heard with stethoscope, and as amount
of bone and cartilage increases, the hardening skeleton can be
detected by ultrasound. By end of 16th week, fetus has assumed a
distinctly human apperance, but no chance of survival outside of
womb. During 5th-6th months, nails haren, skin thickens, and
eyebrows, eyelashes aand scalp hair appear. At 20 weeks, sweat
glands are functionning and fetal heartbeat is often strong enough to
be heard by placing ear on abdomen. Fetus is covered by white cheesy
substance called vernix (protecrs fetal skin against chapping druing
long exposure to amniotic fluid) and fine layer of body hair called
lanugo (helps vernix stick to skin). By end of 6th month, fetus's visual
and auditory sense are clearly functional. (preterm babies born at 25
weeks become alert at sound of loud bell and blink in response to
light). Use of magnetoencephalography (MEG) has revealed that the
fetus has some ability to discriminate between sounds. May indicate
presence of a rudimentary, fetal short-term memory system. Fetus is
about 35-38cm and weight under 1kg.
• The third Trimester: the seventh through ninth months: All organ
systems mature rapdily, preparing fetus for birth. Between 22-28
weeks, fetuses reach the age of viability. Fetal monitoring techniques
revealed that 28- to 32- week-old fetuses begin to show better
organized and more predictable cycles of heart rate activity, gross
motor activity, and sleepiness/waking activity, findings that seem to
indicate that their developping nervous systems are now sufficiently
well organized to allow them to survive if premature birth occurs.
However, fetuses born at this stage still require oxygen assitance b/c
pulmonary alveoli in their lungs are too immature to inflate and exchange gases on their on. By end of 7th month, fetus weight over
1,8 kg and is about 40-43 cm long. By 8th month, it is about 46cm and
put on another 0.5-1 kg; much of this fat comes from fat deposited
under skin that will help insulate baby to changes of temperature. By
middle of 9th month, fetal activity slows and sleep increases. Fetus
starts to position in fetal position, and near cervix. Over the last
month, the uterus contracts, cervix dilates and prepares to give birth.
Environmental Influences on Prenatal Development
The term refers to any disease, drug or other environmental agent that can
harm a developping embryo or fetus by causing physical deformities,
severely retarded growth, blindness, brain damage, and even death. About
95% of newborns babies are perfectly normal and that many those born with
defects have mild, temporary or reversible problems. Effects of a teratogen
on a body part or organ system are worst during period when that structure is
forming and growing most rapidly. Genetic makeup influences the
susceptibility of being affected by a teratogen. Same defect can be cause by
many teratogens; and a variety of defects can be cause by same teratogen.
The longer the exposure (or higher dose); the more serious harm can be
caused. Embryos and fetus can be harmed by fathers' as well exposure too.
The long term effect can depend on the quality of postnatal environment.
Some teratogen cause "sleeper effects" that may appear later in life. Each
major organ has a sensitive period (when it is evolving and developping),
critical periods may especially be between 3-8 weeks of pregnancy. For head
and nervous system, 5th week. Heart is vulnerable 3.5-6.5 weeks. However,
entire prenatal period should be considered as sensitive period for human
development. Teratogens can also influence psychological development.
Alcohol can cause persons to perform lower on IQ tests of cognitive skills.
• Maternal Diseases: some diseases can cross placenta and harm even
more the fetus than the pregant woman herself.
Rubella: has caused pregnant women to deliver blind babies. Also, can
cause deafness, cardiac abnormalities, and mental retardation.
Substantially higher risk for the developmental of psychotic disorders
than did those that were not exposed to rubella. 60-85% of babies
whose mother were exposed had rubella in first 8weeks of pregnancy
will have birth defects, compared to 50% in thirs trimester, and 16%
for those in week 13-20. Sensitive-period principle. Risk of eye and
heart defects are greatest in first 8weeks; deafness when mother is
week 6 through 13.
Other Infectious diseases: toxoplasmosis (parasite found in many animal) by eating undercooked meat or handling animal's feces that
has eaten an infected animal.This cose mild cold-like symtomps in
mother, but for babies in womb, serious brain and eye damage. can
also induce miscarriage.
STIs: capable of pruducing serious birht defects.(genital herpes
• Drugs: Even mild drugs can have lasting efects on developing embryo.
The thalidomide tragedy: mild tranquilizer pregnant women took to
alleviate nausea and vomiting, gave birht to babies with severe
defects. Some even displayed phocomelia (structural abnormality in
which some parts of body missing and Flipper as feet). Effect of drug
depended when it was taken. if 21st days, baby born w/o ears. if 25th-
27th day then no arms. But some mothers also delivered healthy
Other common drugs: Heavy use of aspirin -> fetal growth retardation
poor motor control, infant death. Use of ibuprofen -> in 3rd trimester
increases risk of prolonged delivery and pulmonary hypertension in
babues. heavy use of caffeine -> complications as miscarriage and low
birth weight. Antidepressants (containing lithium)-> can produce heart
defects if takend 1st trimester. Hormones/contraceptive pill ->sligthly
increase of heart defects in embryo. Diethylstillbestrol (DES) sex
hormone -> was prescribed for prevention of miscarriage, but women
17-21 yrs whose mother took it, were at risk of developing rare cervical
cancer and abnormalities of reproductive system. and more likely to
miscarry if get pregnant.
Alcohol: Fetal Alcohol Syndrome (FAS) -> physical and neurobehavioral
defects. Fetal Alcohol Effects (FAE) now as ARND (Alcohol related
neurodevelopmental disorder)-> when neural behavior in absence of
physical defects. can cause microcephaly (small head) and
malformation of heart, limbs, joints and face. babies likely to display
irritab ility, hyperactivity, seizures, and tremors. smaller than normal.
IQ score lower than normal babies. 90% display major adjustment
problems as adolescents and young adults.There is no safe amount of
alcohol that can be consumed during pregnancy! MRI has revealed
structural abnormalities in brain of children with FAD. Depressive
symptoms at age 6, and more present in girls. It can affect male
reproduction aswell, by reducing sperm motility, lower sperm count
and abnormally formed sperm.
Cigarrette smoking: In 3rd trimester is the most negative period for
fetus. A possitive association between smoking in 1st trimester and cleft lip(with or w/o cleft palate). somking retards rate of fetal growth
and increases risk of miscarriage. low-birth babies. Schuetze and
Zeskind (2001) reported that smoking during pregnancy may also
affect the regulation of autonomic activity in neonates. Heart of
neonates beat more rapidly when exposed to nicotine. Nicotine
diffuses rapidly through placenta. (15% more concentrated). Can have
long term effects in cognitive performance, but so far, we only know
until 16yrs of age. (beyond that, no diff. found)
illicit drugs: Variety of cognitive and behavioral defects are associated
with this. exposure to marijuana is associated with changes in
functioning of basal nucleus of amygdala (regulation of emotion). Can
cause behavioral distubrance that put them at risk for adverse
outcomes later in childhood. Will present more symotoms of anxiety
and depression. Women more likely to miscarry. Addicted infants
experiece withdrawal symptoms such as vomiting, dehydration,
convulsions, extreme irritability, weak sucking, high pitched crying.
Babies born who were exposed to drugs, were placed in foster homes
with special care, and showed development improvements.
Environmental factors. Also, boys are more vulnerable to the effects of
maternal prenatal drug abuse. Babies whose mother used cocaine or
crack more likely to be born prematurely with defects; might be
impaired visual-spatial abilities.
• Environmental Hazards:
Radiation: In japan, 75% of pregnant women had babies who died
shortly after when atomic blast happened. Avoid x-rays b/c possibility
of developping complications.
Chemicals and Polluants: So many in our environment. Women
exposed to heavy metals such as lead, zinc, mercury can give birth to
babies with physical health impariment and mental abilities
impairment. PCBs give low weight babies. also associated with
difficulty in maintaining atention, difficulty with spatial reasoning skills
and slower reaction time. 9yr olds who breastfed did even more porrly
(because extended exposure to PCB) in complex task. Can affect
• The mother's diet: before ti was said to gain about 7-8 kg to ensure a
healthy development; but now it is 11-14kg. Severe malnutrition can
disrupt the formation of the spinal cord and induce miscarriages.
During 3rd trimester, more likely to result in low-weight babies, with
small heads and may fail to survive. They show severe cognitive deficits. those who do not gain weight will have irritable temperament.
Dietary suplements with responsive parents can help eliminate long
term damage or prenatal nutrition. In canada, poor women are at risk
for poor nutrition. Programs are established to give nutritional
supplement programs. Also, women may have plenty to eat but fial to
obtain all vitamins and minerals necessary. adding small amount of
magnesium and zinc improves functioning of placenta and reduces
incidence of many birth complications. Dev. organism needs iodine to
ensure normal thyroid functioning. Need folic acid, B-complex vitamin
found in fresh fruits, beans,... to help prevent down syndrome, as well
as spina bifida, anencephaly, and other defects of neural tube. (@
least 0.4mg/day). especially important from time of conception through
first 8 weeks. High dose of vit. A can produce birht defects.
• The mother's Emotional Well-Being: when women become emotionally
aroused, their gland produce adrenaline/ other stress hormones.
Severe emotional stress is associated with low birth weight, premature
delivery, decreased fetal motor activity, other... Dipierto, Costigan and
Gurewitch (2003) found thast increased vbariability in fetal heart rate
and decreased motor activity were associated with increased maternal
stress during task. may be caused by sensory experience fetus has.
babies tend to be highly active, irritable and irregular in their
feeding,sleeping and bowel habits.. Have higher cortisol in blood. Van
der Bergh and Marcoen (2004) long term consquences associated with
sensitive periods can cause ADHD. (12-22 weeks of pregnancy). also
stress can weaken immune system in pregnant women, so can catch
more infectuous diseases. The important thing is her ability to manage
stress, stress at some point in pregnancy (second trimester) is good,
b/c increases motor and mental development at age 2 cause by
glucocorticoids (stress hormone that promotes growth). but all
depends on ability of mother to manage stress.
• The mother's Age: safest time to bear a child is between 16-35 yrs.
younger than 16 experience more complications. To add to this, foten
they are in poor confitions, poor nutrition, impoversihed family
backgrounds. usually not at risk when they receive good health care.
after age 35, incidence of miscarriage. conceiving children with
Prevention of Birth Defects: majority of birthrs are health