Human Growth
and
Development
Chapter Four
Prenatal Development and Birth
PowerPoints prepared by Cathie Robertson, Grossmont College
Revised by Jenni Fauchier, Metropolitan Community College
From Zygote to Newborn
• Germinal period—first 14 days
• Embryonic period—3rd through 8th
weeks
• Fetal period—9th week through birth
Process of Conception
Germinal: The First 14 Days
• Zygote divides and keep dividing (at least
though 3rd doubling they are the same)
• At this stage (8 cells) differentiation begins
- early “stem” cells take on distinct
characteristics
- they gravitate to locations,
foreshadowing the type of cells they
will become
Germinal: The First 14 Days, cont.
• At about a week after conception the multiplying
cells separate into two masses
- outer layer forms a shell (later the placenta) and
the inner cells from a nucleus (later the embryo)
- first task of out cells to achieve implantation—
embed themselves into the nuturant environment
of the uterus
• 60% of all natural conceptions fail to implant; 70%
of in vitro procedures fail to implant
Embryo: From the Third
to the Eighth Week
• First sign of human structure: thin line down
the middle (22 days) that becomes the neural
tube, which eventually forms the central
nervous system, including brain and spinal
column
– fourth week
• head begins to take shape
• heart begins with a miniscule blood
vessel that begins to pulsate
Embryo: From the Third to the Eighth
Week, cont.
– fifth week
• arm and leg buds appear
• tail-like appendage extends from the spine
– eighth week
• embryo weighs 1 gram and is 1 inch long
• head more rounded; face formed
• all basic organs and body parts (but for
sex) present
– 20% of all embryos spontaneously abort now
Fetus: From the Ninth
Week Until Birth
• Called a fetus from 9th week on
Third Month
• Sex organs take shape (Y cell sends signal
to male sex organs; for females, no signal
occurs)
- genital organs fully shaped by 12th week
• All body parts present
• Fetus can move every part of body
• Fetus weighs 3 ounces and is 3 inches long
Middle Three Months:
Preparing to Survive
• Heartbeat stronger
• Digestive and excretory systems
develop more fully
• Impressive brain growth (6X in size
and responsive)
- new neurons develop (neurogenesis)
- synapses—connections between
neurons (synaptogenesis)
Middle Three Months: Preparing
to Survive, cont.
• Age of viability—age at which
preterm baby can possibly survive
(22 weeks)
- 26 weeks survival rate about 50%
. brain maturation critical to viability
. weight critical to viability
- 28 weeks survival rate about 95%
Fetal Brain Maturation
Final Three Months—
Viability to Full Term
• Maturation of the respiratory
and cardiovascular systems
-critical difference
• Gains weight—4.5 lbs. in last 10
weeks
Risk Reduction
• Despite complexity, most babies are born
healthy
• Most hazards are avoidable
• Teratology—study of birth defects
– teratogens—broad range of substances
that can cause environmental insults
that may cause prenatal abnormalities
or later learning abilities
Determining Risk
• Risk analysis—weighing of factors that
affect likelihood of teratogen causing
harm
Timing of Exposure
• Critical period—in prenatal
development, the time when a
particular organ or other body
part is most susceptible to
teratogenic damage
-entire embryonic period is
critical
Amount of Exposure
• Dose and/or frequency
• Threshold effect—teratogen relatively
harmless until exposure reaches a
certain level
Amount of Exposure, cont.
• Interaction effect—risk of
harm increases if exposure to
teratogen occurs at the same
time as exposure to another
teratogen or risk
Genetic Vulnerability
• Genetic susceptibilities: product of
genes combined with stress
• Folic-acid deficiency may cause
neural- tube defects
- occurs most commonly in certain
ethnic groups and less often in
others
• Males are more genetically vulnerable
Specific Teratogens
• No way to predict risk on an individual basis
• Research has shown possible effects of most
common and damaging teratogens
• AIDS and alcohol extremely damaging
– pregnant women with AIDS transmit it
to their newborns; high doses of alcohol
cause FAS; alcohol + drug use increase
risk to developing organism
Low Birthweight
• Low Birthweight (LBW)
– less than 5 1/2 lbs.
• grows too slowly or weighs less than
normal
• more common than 10 years ago
• second most common cause of neonatal
death
• Preterm
– birth occurs 3 or more weeks before
standard 38 weeks
Low Birthweight, cont.
• Small for Gestational Age (SGA)
– maternal illness
– maternal behavior
• cigarette smoking (25% of SGA
births)
– maternal malnutrition
• poorly nourished before and during
pregnancy
• underweight, undereating, and
smoking tend to occur together
Low Birthweight, cont.
• Factors that affect normal prenatal
growth
– quality of medical care, education,
social support, and cultural
practices
The Birth Process
• Hormones in mother’s brain signals
process
• Contractions begin: strong and regular
at 10 minutes apart
– average labor for first births is 8
hours
The Birth Process
The Newborn’s First Minutes
• Assessment—Apgar scale
– five factors, 2 points each
• heart rate
• breathing
• color
• muscle tone
• reflexes
– score of 7 or better: normal
– score under 7: needs help breathing
– score under 4: needs urgent critical care
Variations
• Parents Reaction
– preparation for birth, physical and
emotional support, position and size of
fetus, and practices of mother’s culture
• Medical Attention
– birth in every developed nation has
medical attention
– 22% of births in U.S. are cesarean section
• removal of fetus via incisions in mother’s
abdomen and uterus
– is medical intervention always necessary?
Birth Complications
• Cerebral Palsy—brain damage causing
difficulties in muscle control, possibly
affecting speech or other body
movements
• Anoxia—lack of oxygen that, if
prolonged, can cause brain damage or
death
First Intensive Care . . .
Then Home
• At the Hospital
– many hospitals provide regular
massage and soothing stimulation;
ideally, parents share in caregiving
• At Home
– complications, e.g., minor medical
crises
– cognitive difficulties may emerge,
but high-risk infants can develop
normally
Mothers, Fathers and a
Good Start
• Strong family support (familia)
• Fathers play a crucial role
– may help wives abstain from drugs
or alcohol
– can reduce maternal stress
• Parental alliance—commitment by both
parents to cooperate in raising child
– helps alleviate postpartum
depression
Mothers, Fathers and a Good
Start, cont.
• Parent-infant bond—strong, loving
connection that forms as parents hold,
examine, and feed their newborn
– immediate contact not needed for
this to occur