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Children

Prenatal

Development

3

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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

The Course of Prenatal Development

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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.

The Course of Prenatal Development

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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

The Course of Prenatal Development

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Umbilical cord

Umbilical arteries

Umbilical vein

Uterus

Maternal portion of placenta

Placenta

Fetal portion of placenta

The Placenta and the Umbilical Cord

Fig. 3.2

The Course of Prenatal Development

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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

The Course of Prenatal Development

© 2010 The McGraw-Hill Companies, Inc. All rights reserved.

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

The Course of Prenatal Development

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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

Strategies for Expectant Mothers

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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

Strategies for Expectant Mothers

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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

Strategies for Expectant Mothers

© 2010 The McGraw-Hill Companies, Inc. All rights reserved.

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)

Strategies for Expectant Mothers

© 2010 The McGraw-Hill Companies, Inc. All rights reserved.

Fig. 3.6

Percentage of U.S. Women Using Timely Prenatal Care: 1990 to 2004

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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

Strategies for Expectant Mothers

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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

Hazards to Prenatal Development

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Zygote Embryonic period (wks) Fetal Period (wks)

Period of susceptibility to functional defects

Fig. 3.7 (modified)

1 2 3 4 5 6 7 8 9 16 32 38

Teratogens and Timing of Their Effects on Prenatal Development

Most serious damage

from teratogens in first 2–8

weeks

Period of susceptibility to structural defects

Central nervous system Heart

ArmsEyes

Legs Ears

TeethPalate

External genitalia

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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

Hazards to Prenatal Development

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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

Hazards to Prenatal Development

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Environmental Hazards

• Father’s exposure to lead, radiation

• X-ray radiation

• Pollutants and toxin wastes

• Fertilizers and pesticides

• Lead-based paints

• Petrochemicals

Hazards to Prenatal Development

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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

Hazards to Prenatal Development

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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

Hazards to Prenatal Development

© 2010 The McGraw-Hill Companies, Inc. All rights reserved.

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

Hazards to Prenatal Development

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The End

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