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Prenatal Development: Three time periods
- 1. Pre-embryonic -> up to 3.5 wks (Implanting germ layers)
- 2. Embryonic -> 3.5-9 wks (Organogenisis)
- 3. Fetal -> 9-38 wks (Growth: Length & Wt)
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Definition: Teratology
The study of abnormal embryogenesis and it's causes.
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Definition- Teratogen:
Anything that induces or increases the incidence of congenital malformations
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Classifications of teratogens:
- 1. Infectious agents
- 2. Physical agents
- 3. Chemcal agents
- 4. Hormones
- 5. Maternal health
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Prenatal period most susceptible to teratogens:
Organogenesis
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Pre-embryonic Period
Duration:
Major events/characteristics:
Susceptibility to teratogens:
- Duration: Fertilization through 3.5 wks
- Major events/characteristics: Gastrulation/ body folding -> there can be spontaneous abortions!
- Susceptibility to teratogens: Low
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Embryonic Period
Duration:
Major events/characteristics:
Susceptibility to teratogens:
- Duration: 3.5 wks -> 9th wk
- Major events/characteristics: Organogenesis - complete gastrulation and body folding
- Susceptibility to teratogens: High-most susceptible
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Fetal Period:
Duration:
Major events/characteristics:
Susceptibility to teratogens
- Duration: 9th wk -> birth
- Major events/characteristics: growth & maturation of organ systems
- Susceptibility to teratogens: Less susceptible
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Methods of age measurement:
- Age measurement:
- Crown to Rump Length (CRL): 7-14 wks
- Biparietal diameter (BPD), abdominal circumference, femur length: 16-30 wks
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Fetal Period
29th Week to 20th Week (5 months)
Major events/characteristics:
Major events/characteristics: Swallows, respiratory movements, gender detectable, fetal movements, primary centers of ossification.
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6 months to birth
Major events/characteristics:
Surfactant:
- Major events/characteristics: wt increases
- Surfactant: (coats alveoli) helps lungs to inflate after birth -> very important! Can detect lung maturity with lecithin/spingomyelin ration (L/S)
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Length of Pregnancy
From fertilization:
From Last Menstrual Period (LMP):
Full term birth:
Premature birth:
Postmature birth:
- From fertilization: 38
- From Last Menstrual Period (LMP): 40
- Full term birth: 38 -> 40 wks
- Premature birth: < 38 wks
- Postmature birth: > 40 wks
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Birth Weight:
Normal
Low birth weight:
- Normal: 3200 g
- Low birth weight: < 2500 g
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Definition: IUGR
Effects on fetus:
Possible causes:
- IUGR: In Utero Growth Retardation
- Effects on fetus: neurological deficiencies, respiratory distress syndrome, hypoglycemia, hypokalemia
- Possible causes: teratogens, placenta issues
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Amnion, Amniotic Cavity and Fluid
Formation of Amniotic Cavity-
Start (Week):
Completed (Week):
- Start (Week):
- Completed (Week):
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Amnion:
Amnion: Amnioblasts + extra embryonic mesoderm
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Chorion:
Chorion: Extraembryonic mesoderm + cytroblasts + syncytiotrophoblasts
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Amniochorionic membrane:
Amniochorionic membrane: Fusion of the amnion and chorion at about 12 weeks.
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Amniotic Band Syndrome (ABS):
Amniotic Band Syndrome (ABS): Rupture of the amnion (amniochorionic membrane) that creates chords or bands that can encircle and constrict fetal body parts.
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Amniotic fluid
Amniotic Fluid Functions:
Amniotic Fluid Functions: Cushions and prevents sticking, allows movement (muscular and respiratory), barrier to infections, helps control body temp., helps maintain fluid and electrolyte balance
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