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Kathleen Stassen Berger
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Part I
Prenatal Development and Birth
Chapter Four
From Zygote to Newborn
Risk Reduction
Birth
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From Zygote to Newborn
• Prenatal development is divided into three
main periods:
– germinal period (0-2 weeks)
– embryonic period (3-8 weeks)
– fetal period (9 weeks-birth)
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• germinal period:
– first two weeks of prenatal development after
conception
– Characterized by rapid cell division and the
beginning of cell differentiation.
Germinal: The First 14 Days
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• embryonic period:
– approximately the third through eighth week after
conception
• all body structures, including internal organs,
begin to develop
• fetal period:
– stage of prenatal development from ninth week after
conception until birth, during which the organs grow
in size and mature in functioning
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Germinal: The First 14 Days
• implantation: – process in which
developing organism burrows into placenta that lines uterus
• placenta: – organ that surrounds
developing embryo and fetus, sustaining life via the umbilical cord
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• Embryo:
– name for a developing human organism from about
the third through the eighth week after conception
Embryo: From the Third Through the Eighth Week
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• The developing organism is called a fetus from the start of the ninth week after conception until birth.
• during the fetal period the fetus develops from tiny, sexless creature to a 7 1/2-pound, 20-inch boy or girl
Fetus: From the Ninth Week Until Birth
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• At the end of the third month, the fetus has all its body parts.
• Weighs approximately 3 ounces, and is about 3 inches long.
• Early prenatal growth is very rapid, but there is considerable variation from fetus to fetus, especially in body weight.
The Third Month
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• In the fourth, fifth and sixth months:
– heartbeat becomes stronger
– cardiovascular system becomes more active
– brain increases about six times in size
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• age of viability:
– Age at which a fetus can survive outside the mother’s
uterus if specialized medical care is available.
– about 22 weeks after conception
• In the final three months of prenatal life:
– brain waves indicate responsiveness.
– lungs expand and contract, using the amniotic fluid
as a substitute for air.
– heart valves, arteries, and veins circulate the fetal
blood.
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Risk Reduction
• teratogens: agents and conditions that can:
– harm the prenatal brain
– impairing the future child’s intellectual and
emotional functioning
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• Once it was thought the placenta screened
out all harmful substances.
– Doctors on an Australian military base traced an
increase in blindness among newborns to rubella
(German measles) contracted by pregnant women
a few months earlier.
– Realized that some diseases during pregnancy
could harm a fetus.
Determining Risk
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The effort to understand what triggered such damage gave rise to:
– teratology: science of risk analysis, the study of birth defects
– risk analysis: to determine likelihood of harm, science of weighing the potential effects of a particular:
• event
• substance
• experience
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• Second important factor is the dose and/or
frequency of exposure.
– threshold effect: situation in which a certain
teratogen is relatively harmless in small doses but
harmful once exposure reaches certain level (the
threshold)
– interaction effect: result of a combination of
teratogens
• Sometimes risk is greatly magnified when embryo or
fetus is exposed to more than one teratogen at the
same time.
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Genetic Vulnerability
• Several lines of evidence suggest that genes
may be crucial.
– Dizygotic twins, exposed to same teratogens
but have only half their genes in common, are
born with different abnormalities.
• Suggests both protective and vulnerable
genes.
– Cleft lip, cleft palate, club foot more common
in some families.
• Suggests genetic vulnerability.
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Protective Measures
• Impact of teratogens cannot be predicted
before mid-pregnancy.
• Some pregnant women are exposed to the
tetragons with no evident harm.
• Some defects occur even thought the woman
avoids all known tetragons while pregnant.
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A View From Science
• Alcohol in high doses is a proven teratogen.
• 40 years ago drinking during pregnancy was
believed to be harmless.
• Obstetricians noted that some patients who
drank heavily while they were pregnant had
babies with distorted faces.
– fetal alcohol syndrome (FAS)
– fetal alcohol effects (FAE)
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• fetal alcohol syndrome (FAS): cluster of birth
defects, including:
– abnormal facial characteristics
– slow physical growth
– retarded mental development
• fetal alcohol effects (FAE): condition in which child
has been exposed to alcohol before birth
– has some signs of fetal alcohol syndrome but does not meet
all the criteria
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Benefits of Prenatal Care
• Tests done during pregnancy can diagnose
problems early on, and remedies can be put
in place in some instances.
• sonogram: image of unborn fetus (or an
internal organ) produced by high-frequency
sound waves (ultrasound)
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The Newborn’s First Minutes
• Most newborns begin to breathe as soon as their head emerges.
– first breath causes infant’s color to change
– eyes open wide
– the tiny fingers grab
– toes stretch and retract
– mucus in the baby’s throat is removed
– umbilical cord is cut to detach the placenta
– placenta is expelled
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Apgar scale: quick assessment of newborn’s condition
including:
– the baby’s color
– heart rate
– reflexes
– muscle tone
– respiratory effort
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Medical Intervention
• about 31% of births in the U.S. are
cesarean section, (also called c-section)
– incision through mother’s abdomen and uterus
to allow fetus to be removed quickly, instead of
being delivered through the vagina
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Birth In Developing Nations
• In the U.S. only 1% of births take place at
home.
• Worldwide most births occur at home.
• doula- a woman who helps with the birth
process
- also helps with breastfeeding and newborn care.
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• anoxia: – lack of oxygen that can cause brain damage or
death to the baby
– means “no oxygen”
• cerebral palsy: – disorder that results from damage to brain’s motor
centers
– People with cerebral palsy have difficulty with muscle control, so their speech and body movements are impaired.
Anoxia
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• Average weight of a newborn is 7½ lbs.
– low birthweight (LBW): a body weight at birth of less than 5½ lbs.
– very low birthweight (VLBW): a body weight at birth of less than 3 lbs, 5oz.
– extremely low birthweight (ELBW): a body weight at birth of less than 2 lbs, 3 oz.
Low Birthweight (LBW)
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• preterm birth: occurs 3 or more weeks before full 38 weeks of a typical pregnancy
– Preterm babies are typically (but not always) LBW because they miss final weeks of weight gain.
– small for dates or small for gestational age (SGA)- birth weight is lower than expected given the time of conception.
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Social Support
• The developing person is affected by quality of: – medical care
– education
– culture
– social support
• Fathers and other relatives, neighbors, cultures, and, clinics can reduce risk of birth complications
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Mothers, Fathers, and a Good Start
• Birth complications can have a lingering impact on the new family, depending partly on: – sensitivity of hospital care
– the home
• To reduce stress on an infant who has to stay in the hospital, parents are encouraged to help with early caregiving.
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• kangaroo care: form of child care in which the mother of a low-birthweight infant spends at least an hour a day holding the baby between her breast, like a kangaroo
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Help from Fathers
• Fathers can be crucial in the effort to produce a healthy baby.
• Supportive father-to-be helps a mother-to-be: – stay healthy
– well nourished
– drug-free
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• parental alliance: cooperation between a
mother and a father based on mutual
commitment to their children
• Parents agree to support each other in their
shared parental roles.
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• new mother’s feelings of inadequacy and sadness in days and weeks after giving birth including:
– irritability
– eating disruptions
– sadness
– feeling overwhelmed and inadequate
• affects 10-15% of women
Postpartum Depression