Birth Defects Health Article

Birth Defects

Defects present at birth, resulting from hereditary factors, environmental influences, or maternal illness.

Birth or congenital defects are present at birth and result from hereditary factors, environmental influences, or maternal illness. Such defects range from very minor, such as a dark spot or birthmark that may appear anywhere on the infant's body, to more serious conditions that may result in marked disfigurement or limit the lifespan of the child. A number of factors individually or in combination may cause birth defects. Heredity plays a major role in passing birth defects from one generation to the next. Such conditions as sickle-cell anemia, color blindness, deafness, and extra digits on the hands or feet are hereditary. The condition may not appear in every generation, but the defective gene is usually passed on.

Low birth weight is the most common birth defect, with one in every 15 babies being born at less than their ideal weight. Weights between 5 lb, 8 oz (2,500 g) and 3 lb, 5 oz (1,500 g) are considered low. Low birth weight may occur if the baby is born prematurely, before the normal gestation period of 38 weeks has elapsed, or after a normal gestation period. Premature birth, other than being a birth defect in itself, may also have accompanying effects. A baby born before the 28th week of gestation, for example, may have great difficulty breathing because the lungs have not developed fully.

Prenatal conditions can cause birth defects. For example, the mother's exposure to chemicals such as mercury or to radiation during the first three months of pregnancy may result in an abnormal alteration in the growth or development of the fetus. The mother's diet may also be a factor. A balanced, healthy diet is essential to the proper formation of the fetus because the developing baby receives all of its nutrition from the mother.

Prenatal development of the fetus may also be affected by disease that the mother contracts, especially any that occur during the first trimester (three months) of pregnancy. For example, if a pregnant woman contracts German measles, or rubella, the virus may cross the placenta and infect the fetus. The rubella virus interferes with the fetus's normal metabolism and cell movement and can cause blindness (from cataracts), deafness, heart malformations, and mental retardation. The risk of fetal damage resulting from maternal rubella infection is greatest during the first month of pregnancy (50%) and declines with each succeeding month.

It is especially important that the mother not smoke, consume alcohol, or take drugs while she is pregnant. Drinking alcohol heavily can result in fetal alcohol syndrome (FAS). Newborns with FAS have small eyes and a short, upturned nose that is broad across the bridge, making the eyes appear farther apart than normal. These babies are also underweight at birth and do not catch up as time passes. They often have some degree of mental retardation and may exhibit behavior problems. A mother who continues to use illicit drugs, such as heroin, crack, or cocaine, will have a baby who is addicted to its mother's drug. The addiction may not be fatal, but the newborn will be physically uncomfortable and disagreeable until the addiction is controlled.

Some therapeutic drugs taken by pregnant women have also been shown to produce birth defects. The most notorious example is thalidomide, a mild sedative. During the 1950s women in more than 20 countries who had taken this drug gave birth to more than 7,000 severely deformed babies. These children suffered from a condition called phocomelia, which is characterized by extremely short limbs, often with no fingers or toes.

In 1992, the U.S. Public Health Service published the recommendation that all women of childbearing age consume 0.4 milligrams of folie acid daily to decrease the risk of two common and serious birth defects, spina bifida and anencephaly. The Centers for Disease Control estimates that 50-70% of these birth defects could be prevented if this recommendation were followed before and during early pregnancy. All women between 15 and 45 years of age should consume 0.4 mg of folic acid per day because half of U.S. pregnancies are unplanned and because these birth defects occur very early in pregnancy (3-4 weeks after conception), before most women know they are pregnant.

Following are some of the most common birth defects, ranging from those that cause anatomic changes to those that may prove lethal to the newborn.