Chapter 4Prenatal 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

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LO 7.6 Germinal, embryonic, and fetal periods of pregnancy

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)

– 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 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:

• 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

• 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

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LO 7.6 Germinal, embryonic, and fetal periods of pregnancy

TeratogensThalidomide (for morning sickness)

All or parts of limbs missing

• Sudden Infant Death Syndrome

Fetal Alcohol Syndrome

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Fetal Alcohol Syndrome.• Low birth weight • Developmental delay• Epilepsy• Poor coordination / fine

motor skills • Behavioral problems

2 six week old infants

FASNormal child

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

• 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

• 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