1. © 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Chapter 3
Prenatal Development
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.

2. Periods of Prenatal development
Germinal
Embryonic
Fetal
Teaching Tip: Before they read this chapter, have students generate a list of questions regarding prenatal development. At the end of the chapter have them revisit these questions and see how many they can now answer.
Technology Tip: Have students visit the Baby Center website to learn about a variety of topics related to pregnancy and childbirth.
URL:

3. The Germinal Period
Germinal period: The first two weeks after conception
Creation of the zygote, continued cell division, and the attachment of the zygote to the uterine wall

4. The Germinal Period
Blastocyst: The inner mass of cells that develops during the germinal period
These cells later develop into the embryo
Trophoblast: The outer layer of cells that develops in the germinal period
These cells later provide nutrition and support for the embryo

5. Fertilization/Prenatal Period1 5 14 28

6. FIGURE 3.1 - SIGNIFICANT DEVELOPMENTS IN THE GERMINAL PERIOD

7. The Embryonic Period
The Embryonic Period - Three to eight weeks after conception
The rate of cell differentiation intensifies, support systems for the cells form, and organs appear
Organogenesis
Developmental trends
Cephalocaudal
Proximodistal

8. The Embryonic Period
Endoderm: The inner layer of cells, which develops into digestive and respiratory systems
Mesoderm: The middle layer of cells, which becomes the circulatory system, bones, muscles, excretory system, and reproductive system
Ectoderm: The outermost layer of cells, which becomes the nervous system and brain, sensory receptors and skin parts
Life Support:
Amnion
Umbilical cord
Placenta

9. Human Embryos and Fetuses
Figure 3.2 Human Embryos and Fetuses at Various Stages of Development. Development proceeds in cephalocaudal and proximodistal directions. Development of the head takes precedence over development of the lower parts of the body, enabling the brain to be involved in subsequent developments. Illustration A – G represent changes during the first trimester. Illustrations H and I represent development during the second trimester.

10. THE PLACENTA AND THE UMBILICAL CORD

11. The Fetal Period
The Fetal Period - Begins two months after conception and lasts for seven months on average
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

12. FIGURE 3.3 - THE THREE TRIMESTERS OF PRENATAL DEVELOPMENT

13. FIGURE 3.3 - THE THREE TRIMESTERS OF PRENATAL DEVELOPMENT

14. FIGURE 3.3 - THE THREE TRIMESTERS OF PRENATAL DEVELOPMENT

15. The Brain At birth – 100 billion neurons
Neural tube: first 18–24 days after conception, develops out of the ectoderm
Two birth defects related to a failure of the neural tube to close:
Anencephaly
Spina bifida

16. The Brain At about the fifth prenatal week neurogenesis occurs
Neurogenesis: Generation of new neurons
Neuronal migration
Involves cells moving outward from their point of origin to their appropriate locations and creating the different levels, structures, and regions of the brain

17. Influences during Prenatal Period
Teratogen: Any agent that can potentially cause a physical birth defect
The field of study that investigates the causes of birth defects is called teratology
Teratogens include drugs, incompatible blood types, environmental pollutants, infectious diseases, nutritional deficiencies, maternal stress, advanced maternal and paternal age, and environmental pollutants

18. Influences during Prenatal Period
The time of exposure, dose, and genetic susceptibility to a particular teratogen influence:
The severity of the damage to an embryo or fetus
The type of defect

19. TERATOGENS AND THE TIMING OF THEIR EFFECTS ON PRENATAL DEVELOPMENT

20. THE EXPECTANT MOTHER’S Nutrition and Weight Gain
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

21. RECOMMENDED NUTRIENT INCREASES FOR EXPECTANT MOTHERS

22. 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

23. 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

24. 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)

25. PERCENTAGE OF U.S. WOMEN USING TIMELY PRENATAL CARE: 1990 TO 2004

26. PRESCRIPTION AND NONPRESCRIPTION DRUGS
Prescription and nonprescription drugs, may have effects on the embryo or fetus that the women never imagined
Taking the wrong drug at the wrong time is enough to physically handicap the offspring for life
Prescription drugs that can function as teratogens include antibiotics
Nonprescription drugs that can be harmful include diet pills and aspirin

27. Psychoactive Drugs Psychoactive drugs
Act on the nervous system to alter states of consciousness, modify perceptions, and change moods
Examples include:
Caffeine
Alcohol
Nicotine
Cocaine
Methamphetamine
Marijuana
Heroin

28. 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

29. Environmental Hazards
Father’s exposure to lead, radiation
X-ray radiation
Pollutants and toxin wastes
Fertilizers and pesticides
Lead-based paints
Petrochemicals

30. Maternal Diseases Diseases and infections cross the placenta barrier
Rubella (German measles)
Diabetes
Sexually transmitted infections
Syphilis
Genital herpes
AIDS
HIV infection

31. Other Parental Factors
Maternal diet and nutrition
Folic acid and iron
Fish: PCBs and mercury levels
Maternal age
Highest risks: adolescents, over 35 years
Down syndrome
Emotional states and stress

32. 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 - Down syndrome, dwarfism, and Marfan’s syndrome