STAGES OF PRENATAL DEVELOPMENT
Prenatal development is typically divided into three distinct periods (zygote, embryo, fetus). In reality, these periods represent continuous phases of development, during which the organism, protected and sustained by the amniotic sac, the placenta, the umbilical cord, and after the fifth month, the lanugo, undergoes a systematic series of sequential changes to become increasingly complex and differentiated.The Zygote
The period of the zygote, which lasts about two weeks, extends from fertilization to implantation, when the zygote becomes implanted in the wall of the uterus.The Embryo
The period of the embryo begins at that point and lasts until the eighth week. During this period of rapid growth, most of the important organs and physiological systems develop, and the embryo is quite vulnerable to adverse environmental influences.The Fetus
The period of the fetus extends from the beginning of the third month until birth. Although the major organ systems are well differentiated by this time, the central nervous system continues to develop at a rapid pace, reflexes develop, and regulatory processes and the respiratory system continue to mature. A danger at this time is respiratory distress syndrome; and if the child is born before the age of viability, or at 28 weeks, it may not be developed enough to survive.
THE EFFECTS OF THE PRENATAL ENVIRONMENT ON DEVELOPMENT
During prenatal development, teratogens, agents that produce developmental abnormalities, may affect the growing organism, resulting in physical and mental deviations. Seven general principles summarize the effects of teratogens on prenatal development, indicating that the type, timing, and duration of the teratogen play a role in the outcome as well as the genotypes of the mother and child.Maternal Characteristics
Mothers who have their first child when they are over 35 or under 15 are likely to experience more problems during pregnancy and difficulties during delivery than women between these ages. In both groups, the risks are related to maternal health. Young adolescents are less likely to eat properly or to get prenatal care; older women are more likely to have hypertension, diabetes, alcoholism, and other problems related to age.
Deficiencies in maternal diet are related to increased rates of prematurity, stillbirth, infant mortality, physical and neural defects, and small size. The specific form a defect takes is related to the age at which the malnutrition occurs and its duration. Dietary supplements provided during pregnancy and after birth have been successful at reducing some of these effects, but the extent of the reversibility of such damage is not known. Continued ill effects seem to be related to the mother's history of dietary deprivation, the length and severity of the malnutrition, and continuing adverse nutritional, social, and economic factors following birth.
Maternal emotional disturbance has been related to complications during pregnancy and delivery and to hyperactivity and irritability in infants after birth. It is difficult to discover the causes underlying these relationships because women who are emotionally upset during pregnancy may be poorly adjusted in a variety of ways that affect their caretaking and their infant's adjustment after birth.Diseases and Disorders
A wide range of maternal diseases and disorders can affect prenatal development, including Rh factor incompatibility; high blood pressure; diabetes; rubella; and sexually transmitted diseases such as toxoplasmosis, gonorrhea, syphilis, chlamydia, genital herpes, and acquired immune deficiency syndrome, or AIDS. The effects of maternal diseases are related to the stage of fetal development during which they are contracted, and the length of time that they last.Legal and Illegal Drugs
Mothers who smoke cigarettes or drink alcohol are more likely to bear premature or low-birthweight babies than women who do not smoke or drink. In addition, maternal drinking is related to fetal alcohol syndrome, which results in facial abnormalities, short stature, and mental retardation. Even modest amounts of alcohol and passive smoking have been related to negative effects in the offspring. Moreover, genetic effects of fathers' smoking and drinking may be passed to their offspring.
In the case of illegal drugs like cocaine or heroin, drug-addicted infants may exhibit symptoms that disrupt parenting and result in long-term adverse outcomes for both child and parent. Drug-using mothers may have particular problems dealing with such infants because of their own troubles.
Drugs taken by the mother during pregnancy, whether legal or illegal, may have a negative impact on the developing fetus. Sometimes, as in the case of thalidomide and diethylstilbestrol, the effects of the prescription drug on the infant are not known until much later.
ENVIRONMENTAL TOXINSMedical Interventions in Pregnancy and Childbirth
Some obstetrical medications used to ease pain and sedate women during labor and delivery may affect the newborn's behavior for several days after birth. However, there are often no longer-term effects of such drugs.
BIRTH AND THE BEGINNINGS OF LIFELabor and Delivery
Birth involves a series of changes in the mother that permit the child to move from the womb to the outside world. These include uterine contractions during the first stage of labor that allow the cervix to become large enough for the child's head; the child's descent into the birth canal and emergence out of the canal during the second stage; and the expulsion of the placenta during the third stage. If problems arise before or during the delivery, a cesarean delivery may be performed by removing the baby through an incision in the mother's abdomen. Prematurity and Low Birthweight
Birth complications occur in only about 10 percent of deliveries. Some important birth factors that are related to developmental deviations and mortality are anoxia, or lack of oxygen in the brain, prematurity, and low birthweight. Premature babies may be preterm or small for date. Anoxia, early birth, and low birthweight have been associated with physical, neurological, cognitive, and emotional deficits. Most of these negative effects diminish with age, except in extreme cases. Stimulation programs have been successful with low-birthweight babies in combating the effects of isolation and separation of infant and parents caused by spending the first weeks of life in an isolette.
VULNERABILITY AND RESILIENCE IN CHILDREN AT RISK
According to the concepts of the continuum of reproductive casualty and the continuum of caretaking casualty, both birth complications and the environmental situations into which a child is born may vary greatly along continua that stretch from the most favorable to the least favorable conditions for the child's well-being.
Researchers who have studied the interaction of these continua have found that often early environmental conditions that are more favorable can compensate to some extent for adverse perinatal complications.