Prenatal development and birth
The course of prenatal development
periods
Germinal
First 2 weeks after the
conception.
events
• creation of the zygote, continued cell division
and the attachment of the zygote to the uterine
wall (Implantation)
• blastocyst, the inner cell layer develops.
• trophoblast, the outer cell layer develops. It
provides the nutrition and support for the
embryo.
Embryonic
2-8 weeks after
conception.
• rate of cell differentiation intensifies,
support system for cell forms, and organs
appear.
• zygote becomes the embryo.
• blastocyst becomes the endoderm, which
will develop into digestive and respiratory
system.
• trophoblast divides in two parts, i.e.
ectoderm, the outer most layer and
mesoderm, the middle layer.
• ectoderm will become the nervous system,
sensory receptors, and skin parts.
• mesoderm will become the circulatory
system, bones, muscles, excretory and
reproductive system.
• life-support system for the embryo also
matures and develops rapidly. (placenta,
umbilical cord and amnion- a bag of clear
fluid in which the developing embryo floats.
Fetal
(begins 2 months after
conception and lasts for 7
months, on average)
By 3 months, moves its limbs, head;
opens and close mouth; face, forehead,
eyelids, nose and chin are
distinguishable. It can be identified as a
male or female.
By 4 months, arms and leg movements
can be felt by mothers.
By 5 months, structures of the skins such
as toenails and fingernails will be
formed.
By 6 months, eyes and eyelids are
completely formed. Fine layers of hair
covers head.
Miscarriage and abortion
 During miscarriage embryo separates from uterine
wall and is expelled by the uterus.
 causes may be due to chromosomal abnormalities,
viral or bacterial infections, abnormalities of
reproductive tract.
 In some cases severe trauma can cause spontaneous
abortion.
Maternal characteristics
Mother’s age, nutrition, and emotional states can
affect the prenatal development.
 Infants born to adolescents are often premature and
mortality rate of infants is double that of one born to
mother’s in their 20s.
 Babies with down syndrome are rarely born to
mothers below 30, but risk is considered higher for
the mothers below 18.
 Nutrition is very important too as children born
malnourished mothers are likely to be malformed.
 Emotional states and stresses during pregnancy
leads to physiological changes and production of
adrenaline (usually in response to fear), which
may restrict the blood flow to the uterine area and
may deprive the fetus of adequate oxygen.
 Maternal anxiety during pregnancy in a study was
also associated with infants, who were more
hyperactive and irritable along with feeding and
sleeping problems.
Teratology and hazards to prenatal
development
 The field of study that investigates the causes of birth
defects is called teratology.
 Teratogen is any agent that causes a birth defect.
 The probability of structural defects is greatest early
in the embryonic period.
 During the fetal period they likely to stunt growth or
create problems in the way organs functions.
 For eg, brain is most vulnerable at 15-25 days after
conception, eyes 24-40 days, heart at 24-40 days,
and legs at 24-36 days.
Maternal diseases and conditions
Rubella, syphilis and genital herpes are found to cause death
and deformities in children born to mothers who are infected.
AIDS
 Mothers can infect their offsprings
-during gestation across the placenta.
-during delivery through contact with blood or fluids.
-post-partum through breast feeding.
 Approximately one-third born to infected mothers will
ultimately become infected.
 Babies can be infected and symptomatic or infected but
asymptomatic or not infected at all.
Drugs
 Tranquilizers like thalidomide, taken for morning
sickness are known to cause devastating effects on
fetus. Eg, if a woman takes it on day 26, an arm might
not grow.
 Fetal alcohol syndrome (FAS) is a cluster of
abnormalities that appear in the offspring of the
mothers who drink heavily during pregnancy.
 Fetal and neonatal deaths are higher among smoking
mothers.
 Studies have also shown that exposure to smoking was
related to poor language and cognitive development.
 Mothers who smoked during pregnancy had infants
who were awake more on consistent basis, respiratory
problems, and sudden infant death/ crib death were
found very common among the offsprings of mothers
who smoked during pregnancy.
Environmental hazards
 Radiation can cause gene mutation, an abrupt but
permanent change in genetic material.
 Even radiation from x-rays can affect the fetus.
Birth
Stages of birth
Stage 1
(average of 12-24
hours)
Uterine contractions are 15-20 minutes apart
and lasts up to 12 hours or more.
Contraction comes closer as it progress
increases in intensity.
It dilates the cervix to an opening of 4” for a
baby to move from uterus to birth canal.
Stage 2
Head starts to move through the cervix and birth
(lasts 1 and half hours) canal.
Stage 3
(after birth)
Placenta, umbilical cord and other membrane are
detached and expelled.
Delivery complications
 Precipitate delivery is a delivery that takes place too
rapidly – takes less than 10 minutes to be squeezed
through the birth canal.
 It can disturb infant’s normal flow of blood and the
pressure on infant’s head can cause haemorrhaging.
 if the delivery takes too long, anoxia or the
insufficient supply of oxygen to the infant can take
place.
 Anoxia can cause brain damage.
 The breech position in uterus causes buttocks to
emerge first and can cause respiratory problems.
 Some cannot pass through the cervix and has to be
delivered by a cesarean section (surgical removal
of the baby from the uterus)
The postpartum period
 The postpartum period is the period after delivery.
 It is a time when a woman’s body adjusts, both
physically and psychologically, having completed the
process of childbearing.
Physical adjustments
o Involution is the process by which the uterus returns
to its pre-pregnancy size 5 or 6 weeks after birth.
o Nursing the baby helps to contract the uterus at a
rapid rate.
 Emotional and psychological adjustments
o Many women undergo a postpartum depression and
can have a considerable effect on the infant.