Prenatal Development
Module 9
Biological Beginnings:
Conception
 Ova are released from the ovaries and
travel down the fallopian tubes, where
conception occurs. Development begins
at conception.
 Males produce an average of 300 million
sperm per day. Only 300-500 reach the
ovum.
 Sperm can live for 6 days and ova for one.
The Three Periods of Pregnancy
 Germinal (Period of the Zygote)
– First two weeks, ends with implantation
 Embryonic Period
– 2-8 weeks, organogenesis
 Fetal Period
– 9 weeks – birth (all trimesters)
Period of the Zygote
(Germinal)
 4th day – blastocyst, hollow, fluid filled
ball (60-70 cells)
– Inside, embryonic disk will become
new organism
– Outside, troboblast, protective
covering
Period of the Zygote
(Germinal)
 Within about 1 week of conception,
cell differentiation begins
 Implants (attaches to the uterine wall)
on the 10th to 14th day
Period of the Zygote
(Germinal)
 Troboblast will form the amnion (fluid sac
which regulates temperature and forms a
cushion)
 Will also form the chorion, from which
fingerlike villi or blood vessels emerge and
the placenta forms as they burrow into the
uterine lining.
Embryonic Period – 3rd week
after conception
 Umbilical cord connects the growing
organism to the placenta
 It has one vein and two arteries
 The mother’s and embryo’s blood will not
mix directly (red blood cells, bacteria,
hormones, maternal waste are filtered)
Embryonic Period – 3rd week
after conception
 Embryonic disk forms:
– Ectoderm – skin and nervous
system
– Mesoderm – muscles, skeleton,
circulatory system
– Endoderm – digestive system,
lungs, urinary tract, glands
Embryonic Period (2-8
weeks) - Organogenesis
 Neural tube develops first, will become
brain and spinal cord
 Next, heart begins to pump blood
 The basic structure of all the organ
systems grows
 Eyes, ears, nose, jaw, neck, arms legs,
fingers & toes form
 At the end of this period, it weighs less
than one ounce, about one inch long.
Period of the Fetus – Growth and
Finishing Phase – 3rd Month
– The fetus can kick, bend its arms, form a fist,
curl its toes, open its mouth, suck its thumb,
smile & swallow
– By 12th week external genitals well formed,
also fingernails, toenails, tooth buds, eyelids
– Heartbeat can be heard with a special
stethoscope
– End of 3 months, 3 inches, 3 ounces
Period of the Fetus – Growth and
Finishing Phase
 Called a fetus from the 8th week until birth
 Fetus means fully-formed human being because
all organ systems are now in place
 During the 3rd month (12-16 weeks) it will have
coordinated movements, be able to roll over in
the amniotic fluid
 Hair, eyelashes, eyebrows will grow
Period of the Fetus – Growth and
Finishing Phase – 2nd Trimester
– Mother can feel movements
– Can hear heartbeat with ordinary
stethoscope
– Neurogenesis proceeds rapidly
(250,000 neurons per minute)
– At 20-weeks can be stimulated/irritated
by sound; will shield eyes during
Period of the Fetus – Growth and
Finishing Phase-Age of Viability
– Age at which the fetus can survive
outside the mother (38-40 weeks is
full term)
– 5% survive at 22 weeks
– 50% survive at 26 weeks (6 months)
– 95% survive at 28 weeks
Problems with Preemies
– Depends upon gestational age at
birth
– Breathing
Hyaline membrane disease
– Regulating blood oxygen levels
– Apnea
– Temperature regulation
– Feeding
– Parenting – 40% faster weight gain &
brain development with touch
Kangaroo care
Fetal Period – 3rd Trimester
– Begins sleep-wake pattern
– Responsiveness, can feel pain
after 24 weeks
– React to sounds
– Prefer mother’s voice
– Adds fat (5 pounds)
– Receives antibodies
– Assumes birth position (head
down)
Teratogens (Monsters)
– Any environmental agent that causes prenatal
damage (leading to birth defects)
– Types – drugs, diseases, radiation,
environmental pollutants
– Factors – dose, resilience (heredity), number
of teratogens, gestational age at exposure
(embryonic period worst)
Teratogens - Drugs
 Examples
– Thalidomide – 7000 infants affected
Limbs, heart, ears, kidneys, genitals
– DES (diethylstilbestrol) – reproductive
problems in adult children (cancer;
abnormalities in reproductive organs)
Teratogens - Drugs
– Don’t take anything without
consulting your obstetrician
 Examples
– Aspirin – may be associated with
LBW, infant death, lower IQ, poor
motor development
– Caffeine – LBW, miscarriage,
irritable infants
Teratogens – Illegal Drugs
– Cocaine
– Heroin/methodone
Prematurity, LBW, breathing
difficulties, physical defects, infant
death, stressed and drug addicted
– Marijuana
Smaller head size, disturbed
sleep, inattention in infancy
Teratogens - tobacco
Nicotine constricts blood vessels and
lessens blood flow to the uterus, causes
the placenta to grow abnormally, reduces
the transfer of nutrients, raises the carbon
monoxide concentration in the blood
stream which may damage the central
nervous system
Smoking during pregnancy is associated with
LBW and increased frequency of
prematurity, impaired breathing during
sleep, infant death and childhood cancer.
Teratogens - Alcohol
Fetal Alcohol Syndrome (FAS/FAE) is the
leading preventable cause of mental
retardation.
Other symptoms include impaired motor
coordination, attention, memory &
language; slow physical growth &
overactivity.
Facial abnormalities include widely spaced
eyes, short eyelid openings, thin upper lip,
small head, small upturned nose.
Teratogens - Alcohol
Lesson – Women should avoid alcohol
during pregnancy.
Alcohol inteferes with brain
development – causing abnormalities
in structure and function.
Oxygen needed for cell growth is
taken from the fetus to metabolize
alcohol.
Environmental Teratogens
 Radiation (Hiroshima, Nagasaki,
Chernobyl)
– Miscarriages, babies with
underdeveloped brains, physical
deformities, slow growth
 Mercury – 1950s Minamata, Japan –
resulting brain damage in children
 Lead – prematurity, LBW, brain damage,
physical defects
 PCBs (insulators for electrical equipment)
– lower intelligence
Teratogens –
Infectious diseases
Rubella
HIV/AIDS
Genital herpes
toxoplasmosis
Other Maternal Factors
Nutrition
Emotional stress
Maternal age & previous
births
Prenatal Health Care
18% of women in the U.S. wait until the
second trimester, and 4% until the end
to get care
Many of these are unmarried,
adolescent, or poverty stricken.
Reasons include lack of insurance,
ambivalent feelings, high risk behaviors,
and lack of transportation.
Approaches to Childbirth
 How much medical care/availability?
 Should it be natural or prepared?
 How about the epidural?
 How about a midwife (or a doula)?
The Birth Process
– Dilation and effacement (of the
cervix)(Labor)
At
transition a clear channel
from the uterus to the vagina is
formed (birth canal)
– Birth of the baby (Delivery) 20-50
minutes
– Delivery of the placenta (afterbirth)
(5-10 minutes)
Birth Complications and
Medical Interventions
– Anoxia
– Breech position
– Cerebral palsy
– Fetal monitors
– Medication (90-95% of births)
Analgesics,
anesthetics
– Cesarean delivery (30% of births)
Low Birthweight Infants (LBW)
(Low)Birthweight
is the best available
predictor of infant survival & healthy
development.
Low
Birthweight Babies weigh less than
5.5 pounds.
–1 of 14 American infants
–More problems with inattention,
overactivity, language delays, low
IQ scores, and motor deficits
Low Birthweight Infants (LBW)

–Preterm babies – born early
(35 or fewer weeks) may be
weight appropriate
–Small-for-date babies have
more serious problems.
Apgar (1 & 5 minutes after
birth)
 5 characteristics
– Heart rate, respiratory effort, reflex
irritability, muscle tone, color)
– 0,1,or 2 points on each
Total score
– 7+, good physical condition
– 4-6, baby requires assistance
– 3-, infant in serious danger, requires
emergency attention
The Newborn - Arousal
 Sleep 18-20 hours per day
 50% is REM sleep
 SIDS (Sudden Infant Death
Syndrome)