Chapter 4
Prenatal Development and Birth
Chapter 4- Prenatal Development
• Time of fastest development
• Conception
– Ova (eggs) travels from ovary to uterus
– Penetration by 1 of 300-500 sperm
– ZYGOTE (fertilized egg)
Prenatal Development and the Zygote
LO 7.6
Germinal, embryonic, and fetal periods of pregnancy
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Prenatal Stages
Germinal period: days 1-14 (0 - 2 weeks)
– Zygote’s implantation into uterine wall: 1/2 are
successful
– Zygote divides many times through mitosis to form
blastocyst (about 150 cells)
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– Miscarriage: 8-30% (recognized) to 33%
(unrecognized)
Embryonic period: 3rd to 8th week (3rd week - 2nd month)
– Organogenesis – every major organ takes shape
– Sexual differentiation – begins during 7th & 8th week
Outer Layer of Blastocyst (150 cells) forms:
• Amnion – a watertight membrane that fills with
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fluid that protects the embryo
Placenta – provides nourishment by mother’s
blood vessels
Umbilical cord – connection between embryo and
mother
Placental barrier – protects developing child from
many harmful substances, and allows small
molecules exchanged
Inner cell mass of blastocyst forms:
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Ectoderm – (brain and spinal cord)
Mesoderm – muscle tissue, cartilage, bone,
heart, arteries, kidneys, and gonads
Endoderm – gastrointestinal tract, lungs, and
bladder
Neural plate forms neural tube (bottom is spinal
cord)
Top of tube forms into forebrain, midbrain,
hindbrain
Figure 4.3
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Fetal period: 9th week – birth
– Proliferation of neurons (250,000 per minute)
– Migration of neurons
– Differentiation of stem cells
Age of viability – around 23-25 weeks (fetus has possibility
of surviving outside uterus)
3rd Trimester – myelination
Prenatal Development and the Newborn
40 days
45 days
2 months
4 months
Prenatal Environment
• Teratogen: harmful environmental agent
– Harms the developing fetus
– Critical Period: Organogenesis
– Dosage & duration
– Genetic make-up: susceptibility
LO 7.6
Germinal, embryonic, and fetal periods of pregnancy
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Teratogens
Thalidomide (for morning sickness)
All or parts of limbs missing
• Sudden Infant Death
Syndrome
Fetal Alcohol Syndrome
• Low birth weight
• Developmental delay
• Epilepsy
• Poor coordination /
fine motor skills
• Behavioral problems
“Copyright© Allyn & Bacon 2006”
2 six week old infants
Normal child
FAS
Teratogens - Diseases
• Rubella (German Measles)
– Blind, deaf, heart, brain
• Syphilis:miscarriage, blind, deaf, heart, brain
– After 18th week
• AIDS mothers transmit to babies (15%-35%)
– Prenatally, perinatally, postnatally
Teratogens – Environmental Hazards
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Radiation: MR, leukemia, cancer, mutations,
spontaneous abortions, etc.
– Avoid X-rays when pregnant
Pollutants
– In air and water
– Lead - MR (also postnatally)
Anoxia – Oxygen shortage –can cause mental
retardation or cerebral palsy
Postnatal Depression
• Baby Blues, mild, common
• Postpartum depression: 1/10
– Previous depression common
• Children of depressed mothers
– Insecurely attached, less responsive
– Negative to other children
APGAR TEST
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Provides a quick assessment of the newborn’s:
1)Heart rate (0-2 points)
2)Respiratory effort (0-2 points)
3)Muscle tone (0-2 points)
4)Color (0-2 points)
5)Reflex irritability (0-2 points)
The Apgar test is given immediately and 5 minutes after birth
7 or higher = good shape
4 or lower = at risk
The Neonatal Environment
• Culture, early socialization, health status
– E.g., low birth-weight babies (8% in US)
• Less than 5 1/2 lbs or 2500 grams
• Strongly linked to low SES
• Environment: neonatal intensive care
• Risk: blindness, deafness, CP, autism,
cognitive, and later academic problems