Chapter 4 | Prenatal Development and Birth 157genotype across developing organisms. So this is another example of the active child effect, which precedes consciousness and choice. Looking next at nature and nurture interactions, it would be difficult to pinpoint any aspect of prenatal development or birth that did not involve the reciprocal interaction of nature and nurture on development. Returning to the teratogen example, the principles of teratogenic effects, taken together, represent an integration of biological influences and environmental influences. One does not operate without the other. Even the birth process represents an interaction of nature and nurture. There is a strong biological determinism about the birth process, proceeding through each stage in order and with little potential for interruption or interference from the environment during a normal birth. But the environment surrounding the birth clearly influences the health of the baby and the mother, and the feelings of bonding and engrossment that the parents feel for their new baby. We encountered three different qualitative stage progressions in this chapter. First, the developing organism proceeds through three qualitatively distinct stages in prenatal development: the zygote, the embryo, and the fetus. Second, the pregnant woman goes through three qualitatively distinct stages during pregnancy: the first, second, and third trimesters. (And remember that the stages of the developing organism do not correspond chronologically to the pregnant woman’s stages.) Finally, we saw that the birth process can be divided into three qualitatively distinct stages: labor, birth, and afterbirth. As usual, however, we can also see quantitative change in prenatal development. For example, the period of the fetus consists mainly of quantitative changes as the organism grows in size and refines the structures and functions that first develop in the period of the embryo. Finally, we can consider the holistic nature of child development when we recall that prenatal development affects a child’s future physical development as well as cognitive and emotional development, especially in cases in which teratogenic effects interfere with these aspects of development. We saw many examples of problems in prenatal development causing later mental retardation, and some cases of emotional disturbances. When examining the birth process we saw that emotional and social support for the woman giving birth was just as important as the physical assistance she needs with this process. And after birth, parents who are trained to respond to and engage their infants in social interaction are more likely to have infants who are able to overcome early physical complications. In sum, we saw evidence for each of the enduring developmental themes in our examination of prenatal development and birth. Perhaps now it is easier to see that the developing organism is active in its own development, that it moves through a series of both qualitative and quantitative changes as it develops, that both nature and nurture play important roles in the prenatal period, and that we must always consider the child holistically. SUMMARY From Conception to Birth ■ Prenatal development is divided into three phases: ■ The period of the zygote lasts about 2 weeks, from conception until the zygote (or blastocyst) is firmly implanted in the wall of the uterus. ■ The inner layer of the blastocyst will become the embryo. ■ The outer layer forms the amnion, chorion, placenta, and umbilical cord—support structures that help to sustain the developing prenatal organism. ■ The period of the embryo lasts from the beginning of the third through the eighth week of pregnancy. ■ This is the period when all major organs are formed and some have begun to function. ■ The period of the fetus lasts from the ninth prenatal week until birth. ■ All organ systems become integrated in preparation for birth. ■ Fetuses move and begin to use organ systems during this period in preparation for the use of those systems after birth. Potential Problems in Prenatal Development ■ Teratogens are external agents such as diseases, drugs, and chemicals that can harm the developing organism. ■ Teratogenic effects are worst when a body structure is forming (usually during the period of the embryo) and when the “dose” of the teratogen is high. ■ Teratogenic effects differ for different genotypes. One teratogen can cause many birth defects, and different teratogens can cause the same birth defect. pregnant woman should be given a pass from which of the following household chores? a. ■ Fathers are often engrossed with their newborns. fetus c. chorion c. ■ Many mothers feel exhilarated shortly after birth if they have close contact with their babies and begin the process of emotional bonding with them. Some teratogens cause “sleeper effects” that may not be apparent until later in the child’s life. blastocyst b. Potential Problems at Birth ■ Anoxia is a potentially serious birth complication that can cause brain damage and other defects. administered a few days later. in large doses. washing dishes with antibacterial soap b. ■ Interventions to stimulate these infants and to teach their parents how to respond appropriately to their sluggish or irritable demeanor can help to normalize their developmental progress. interfering with positive developmental outcomes. second trimester c. c. ■ Women who abuse alcohol and drugs. Answers appear in the Appendix. Not all embryos or fetuses are equally affected by a teratogen. ■ Pregnant women under severe emotional stress risk pregnancy complications. To protect the prenatal organism against the effects of toxoplasmosis. ■ Maternal characteristics also influence prenatal development. Birth and the Perinatal Environment ■ Childbirth is a three-step process: ■ It begins with contractions that dilate the cervix (first stage of labor). During which trimester of pregnancy does the developing organism pass through the periods of the zygote. ■ Malnourished babies are often irritable and unresponsive. The effects of a teratogen on a body part or organ system are worst during the period when that structure is forming and growing most rapidly. ■ The support of fathers during pregnancy and childbirth can make the birth experience easier for mothers. Some teratogenic effects (like those from DES) are not apparent at birth but become apparent later in a child’s life. ■ Small-for-date babies usually have more severe and longer-lasting problems than do preterm infants. ■ Labor and delivery medication given to mothers to ease pain can. ■ And finally the afterbirth is expelled (third stage of labor). ■ Supplements of folic acid help to prevent spina bifida and other birth defects. the more likely it is that serious harm will be done. ■ The Apgar test is used to assess the newborn’s condition immediately after birth. Mild anoxia usually has no long-term effects. The longer the exposure to or the higher the dose of a teratogen. CHAPTER 4 PRACTICE QUIZ Multiple Choice: Check your understanding of prenatal development and birth by selecting the best choice for each question. Which period of prenatal development is characterized by rapid growth and refinement of all organ systems? a. cleaning the cat’s litter box c. The _________ is an organ formed from the lining of the uterus and the chorion that provides for respiration and nourishment of the prenatal organism and the elimination of its metabolic wastes. ■ These are followed by the baby’s delivery (second stage of labor). 5. embryo d. changing burned-out lightbulbs and other work with electrical fixtures . ■ The problems stemming from both prenatal and birth complications are often overcome in time. The concept of sensitive periods in prenatal development best illustrates which of the following principles of the effects of teratogens? a. third trimester d. or who receive poor prenatal care risk delivering preterm or low-birth-weight babies. and fetus? a. fourth trimester 4. amnion b. embryo. provided that the child is not permanently brain damaged and has a stable and supportive postnatal environment in which to grow. b. vacuuming d.158 Part Two | Biological Foundations of Development ■ Teratogenic effects can be altered by the postnatal environment (through rehabilitation efforts). interfere with the baby’s development. d. who smoke. is a more extensive measure of the baby’s health and well-being. placenta d. first trimester b. zygote 3. ■ Pregnant women who are malnourished (particularly during the third trimester) may deliver a preterm baby who may fail to survive. a. ■ Complications are also more likely among women over 35 and teenage pregnant women who lack adequate prenatal care. ■ The Neonatal Behavioral Assessment Scale (NBAS). 1. umbilical cord 2.