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

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: http://www.babycenter.com/

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

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

Fertilization/Prenatal Period 1 5 14 28

FIGURE 3.1 - SIGNIFICANT DEVELOPMENTS IN THE GERMINAL PERIOD

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

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

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.

THE PLACENTA AND THE UMBILICAL CORD

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

FIGURE 3.3 - THE THREE TRIMESTERS OF PRENATAL DEVELOPMENT

FIGURE 3.3 - THE THREE TRIMESTERS OF PRENATAL DEVELOPMENT

FIGURE 3.3 - THE THREE TRIMESTERS OF PRENATAL DEVELOPMENT

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

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

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

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

TERATOGENS AND THE TIMING OF THEIR EFFECTS ON PRENATAL DEVELOPMENT

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

RECOMMENDED NUTRIENT INCREASES FOR EXPECTANT MOTHERS

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

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

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)

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

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

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

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

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

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

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

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