During the normal development of the individual from conception to maturation, interruptions may occur that result in retardation. These exogenous causes will be discussed according to when they occur-prenatal, perinatal, or postnatal.
The primary prenatal physical causes of retardation are infections and trauma. During the nine months of pregnancy the fetus develops from one cell to a fully functioning body with a brain and all organs in proper order. An interruption of this normal development affects the part of the body that is growing at the time. Most infections are invented from reaching the fetus by the placenta. Rubella, or German measures, is the only acute infection commonly acquired during pregnancy that is not blocked by the placenta. This acute infection disrupted the normal development and results in severe damage and deformity. In one study of 153 children whose mothers contracted rubella during pregnancy, one-half evidenced borderline to severe mental retardation. Deafness, blindness, and heart defects are common.
Trauma includes drugs; maternal undernutrition; radiation; Rh blood incompatibility; chronic maternal infections such as certain viruses, bacteria, and protozoa; and various disorders such as maternal anemia, high blood pressure, and diabetes. Treatment during pregnancy and at birth may reduce the severity of effects in many of these cases.
Perinatal problems, those occurring during the birth process, including prematurity, anoxemia, and direct injury to the head. Premature infants are those born weighing less than 5 1/2 pounds. Babies weighing about 3 pounds at birth stand a greater chance of developing more slowly and evidencing lower intellectual abilities. Anoxemia, or oxygen deprivation, occurs when the placenta is blocked at birth or spontaneous breathing does not occur. In several studies with rhesus monkeys deprived of oxygen at birth, up to 7 minutes of deprivation had no noticeable effect on later functioning. The breech or transverse birth may increase the likelihood of suffocation, but the physician is usually able to turn the baby properly. Direct trauma to the head may arise from a quick birth through a narrow cervical opening. Evidence is scanty for mechanical damage to the head using forceps. It has been suggested that poorly adjusted mothers tend to blame the child's problems on the birth process rather than seeing them as a response to her or the family's tensions.
Postnatal hazards include head injury, asphyxiation, poisons, malnutrition, infections, and brain tumors. Automobile accidents and child abuse are the two most common causes of severe head injury in young children. Meningitis, a viral infection of the brain's lining membrane, and high, persistent fever may affect the brain. These are treatable, and it is usually in several cases that lingering effects will be noted. Asphyxiation may result in brain damage, depending on the length of time of oxygen deprivation.