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3
Children
Prenatal
Development
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The Course of Prenatal Development
The Germinal Period
• First two weeks after conception
– Creation of zygote
– Blastocyst
• inner layer of cells
• develops into embryo
– Trophoblast
• outer layer of cells that develops during
germinal period, nourishes embryo
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The Course of Prenatal Development
The Embryonic Period
• Two to eight weeks after conception
• Cell differentiation occurs, embryo has
three layers of cells
– Endoderm: inner layer of cells form digestive
and respiratory
– Ectoderm: outermost layer forms skin parts,
nervous system, and sensory receptors
– Mesoderm: middle layer forms circulatory,
bones, muscles, reproductive systems, etc.
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The Course of Prenatal Development
Embryo’s Life-Support System
• Placenta
– intertwines but does not join mother and baby
• Umbilical cord
– connects baby to placenta
• Amnion and amniotic fluid
– provides baby’s environment
• Organogenesis
– organ formation
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The Course of Prenatal Development
The Placenta and the Umbilical Cord
Uterus
Umbilical
cord
Placenta
Umbilical
vein
Umbilical
arteries
Fetal portion
of placenta
Fig. 3.2
Maternal portion
of placenta
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The Course of Prenatal Development
The Fetal Period
• Begins two months after conception; lasts
about seven months, until birth
• Largest prenatal size and weight gains
• Fingers, toes, skin, features, lungs, other
structures, and reflexes all develop to
prepare for birth
• The three trimesters are not the same as
the three prenatal periods
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The Course of Prenatal Development
The Brain
• At birth – 100 billion neurons
• Basic architecture assembled during first
two trimesters
– Neural tube: first 18–24 days
– Neurogenesis
– Neuronal migration: 4–6 weeks after conception
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Strategies for Expectant Mothers
Nutrition and Weight Gain
• Nutrition
– Need for protein, iron, vitamin D, calcium,
phosphorus, magnesium increases 50 percent,
water is essential
• Weight Gain
– 25 to 35 pounds associated with best
reproductive outcomes
– Inadequate and excessive weight gain may
affect baby birth weight or mother’s health
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Strategies for Expectant Mothers
Exercise During Pregnancy
• Decrease duration and intensity as
pregnancy progresses
• Avoid high-risk activities
– Warm up, stretch, cool down
– Reduce exercise significantly in last four weeks
• Several studies show exercise during
pregnancy not linked to preterm birth
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Strategies for Expectant Mothers
Prenatal Care
• Prenatal care varies enormously in
– Education
– Screening for manageable conditions and
treatable diseases
– Information on risks and choices before,
during, and after pregnancy
• Good prenatal care makes a difference
– Reduces mortality, physical problems later
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Strategies for Expectant Mothers
Prenatal Care
• Other countries outside the U.S.:
– Have lower rate of low-birth-weight infants
– Free or low-cost prenatal and postnatal care
– Enjoy liberal paid maternity leave
• Factors affecting prenatal care in U.S.
– Individual and social characteristics
– Inadequacy of health care system
– Age group differences (adolescents, adults)
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Percentage of
U.S. Women
Using Timely
Prenatal Care:
1990 to 2004
Fig. 3.6
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Strategies for Expectant Mothers
Cultural Beliefs About Pregnancy
• Conflict between cultural tradition and
Western medicine during pregnancy
– Food craving satisfaction
– Hot-cold theory of illness
– Extended family involvement
– Stoicism valued by many Asians
– Pregnancy as a natural occurrence or a
medical condition
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Hazards to Prenatal Development
Some General Principles
• Teratogen
– Any agent that causes a birth defect
– Severity and type of defect affected by
• Dose, genetic susceptibility, time of
exposure
• All drugs (prescribed, illegal) can have
effects on unborn fetus
– Antibiotics, analgesics, asthma medications
– 1961: thalidomide tragedy
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Teratogens and Timing of Their Effects
on Prenatal Development
Zygote
1
2
Most
serious
damage
from
teratogens
in first 2–8
weeks
Embryonic period (wks)
3
4
5
7
8
9
16
32
38
Central nervous system
Heart
Arms
Eyes
Legs
Ears
Period of susceptibility
to structural defects
Period of susceptibility
to functional defects
Fig. 3.7 (modified)
6
Fetal Period (wks)
Teeth
Palate
External genitalia
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Hazards to Prenatal Development
Psychoactive Drugs
• Psychoactive drugs
– Act on nervous system and change moods
– Alter states of conscious, modify perceptions
– Extent of risk and harm varies
• Use of caffeine, nicotine, and alcohol
• Fetal alcohol spectrum disorders (FASD)
• Dangers of second-hand smoke
• Cocaine and heroin
• Methamphetamine and marijuana
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Hazards to Prenatal Development
Incompatible Blood Types
• Poses risk to prenatal development
– Between mother and father
– Between mother and baby
– Blood groups (A, B, O, AB)
– Rh factor (positive, negative)
– Vaccine within 3 days of birth
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Hazards to Prenatal Development
Environmental Hazards
• Father’s exposure to lead, radiation
• X-ray radiation
• Pollutants and toxin wastes
• Fertilizers and pesticides
• Lead-based paints
• Petrochemicals
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Hazards to Prenatal Development
Maternal Diseases
• Diseases and infections cross the placenta
barrier
– Rubella (German measles)
– Diabetes
• Sexually transmitted infections
– Syphilis, Genital herpes
– AIDS, HIV infection
• New medications and vaccines available
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Hazards to Prenatal Development
Other Parental Factors
• Maternal diet, nutrition, and weight
– Folic acid and iron
– Fish: PCBs and mercury levels
• Maternal age
– Highest risks: adolescents, over 35 years
– Down syndrome
• Maternal emotional states
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Hazards to Prenatal Development
Other Parental Factors
• Paternal factors
– Father’s diet and low vitamin C
– Drug use effects on sperm
– Smoking – effects of second-hand smoke
– Father’s age at conception
• Birth defects: dwarfism, Marfan’s Syndrome
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3
The End
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