Transcript Slide 1

Prenatal Development
Chapter 2
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)
 Within about 1 week of conception,
cell differentiation begins
 Implants (attaches to the uterine wall)
on the 10th to 14th day
Embryonic Period (2-8
weeks) - Organogenesis
 Neural tube develops first, will become
brain and spinal cord – rapid neuron
growth, weak brain waves
 Next, heart begins to pump blood
 The basic structure of all the organ
systems grows
 Eyes, ears, nose, jaw, neck, arm and leg
buds
 At the end of this period, it weighs less
than one ounce, about one inch long.
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 – 3rd Month
– 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
– The fetus can kick, bend its arms, form a fist,
curl its toes, open its mouth, suck its thumb,
smile & swallow
Period of the Fetus – Growth and
Finishing Phase – 2nd Trimester
– Neurogenesis, which begins earlier,
proceeds rapidly (250,000 neurons per
minute)
– At 20-weeks can be stimulated/irritated by
sound; will shield eyes during fetoscopy
Period of the Fetus – Growth and
Finishing Phase-Age of Viability
– The current age of viability (at which the
fetus can survive outside the mother) is
about 22 weeks
– 50% survive at about 25 - 26 weeks (6
months)
– 95% survive at 31+ weeks
Problems with Preemies
– Depends upon gestational age at
birth
– Breathing
Hyaline membrane disease
– Regulating blood oxygen levels
– Apnea
– Temperature regulation
– Feeding
– Parenting – 47% faster weight gain &
brain development with touch
Kangaroo care
Fetal Period – 3rd Trimester
– Begins sleep-wake pattern
– Responsiveness, can feel pain
after 22 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 – Why does it do
this – 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.
Teratogens –
Infectious diseases
Rubella
HIV/AIDS
Genital herpes
toxoplasmosis
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?
– Lamaze, Bradley, hypnobirthing
 How about the pain?
– Epidural, walking/dual-spinal epidural
 How about a midwife (or a doula)?
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
(35/8 or fewer weeks) may be
weight appropriate
–Small-for-date babies may
have more serious problems.
Why so many preemies?
 50% unknown
 Mother’s reproductive system
– Immaturity; twins
 Correlation with Father’s age (older
fathers)
Premature Infants
 Low birthweight
 Very low birthweight -, 1250 grams
 Many will end up normal
 A higher frequency will have minor
problems that show up later