Birth Defect

Like most expectant parents, you probably alternate between fantasies about a healthy baby and worries that your baby will have a health problem. Or perhaps you've been told through prenatal screening that your baby might be born with a birth defect. Many parents assume that all birth defects are severe or even fatal, but the fact is that many are treatable, often immediately after birth — and sometimes even before the baby is born.

It's especially important to know the risk factors involved and how to prevent birth defects. However, it's also important to realize that most babies born with congenital defects are born to two healthy parents.

About Birth Defects

Birth defects are defined as abnormalities of structure, function, or body metabolism that are present at birth. Major birth defects are abnormalities that lead to developmental or physical disabilities or require medical or surgical treatment. There are more than 4,000 different known birth defects, ranging from minor to serious, and although many can be treated or cured, they're the leading cause of death in the first year of life.

According to the March of Dimes, about 150,000 babies are born with birth defects each year in the United States. The American College of Obstetricians and Gynecologists (ACOG) says that 3 out of every 100 babies born in the United States have some kind of major birth defect. Birth defects can be caused by genetic, environmental, or unknown factors. For most birth defects, the cause is believed to be an interaction of a number of genetic and environmental factors.

Structural or metabolic defects are those in which a specific body part is missing or formed incorrectly; metabolic birth defects are those in which there is an inborn problem in body chemistry. The most common type of major structural defects are heart defects, which affect 1 in 150 babies in the United States. Other common structural defects include spina bifida, cleft palate, clubfoot, and congenital dislocated hip.

Metabolic defects affect 1 in 3,500 babies and usually involve a missing or incorrectly formed enzyme (a protein necessary for processing chemical substances in the body). Most children with a metabolic birth defect do not have any visible abnormalities, but metabolic defects are usually harmful or can be even fatal. Metabolic defects include Tay-Sachs disease, a fatal disease that affects the central nervous system, and phenylketonuria (PKU), which affects the way the body processes protein.

Defects caused by congenital infections result when a mother gets an infection before or during the pregnancy. Infections that can cause birth defects include rubella (German measles), cytomegalovirus (CMV), syphilis, toxoplasmosis, Venezuelan equine encephalitis, parvovirus, and, rarely, chickenpox. None of these affect 100% of babies whose mothers are infected during pregnancy. If the mother is infected during early pregnancy, rubella carries the highest risk for birth defects (approximately 20%). Because of nearly universal immunization in the United States, rubella is very, very rare and the congenital rubella syndrome is almost never seen. CMV is probably the most common congenital infection and may be associated with intellectual disability (mental retardation) and hearing loss.

Other causes of birth defects include alcohol abuse by the mother. Although a few medications, such as medicines used for epilepsy, are associated with increased risks for certain birth defects, most commonly prescribed drugs are not associated with a significant risk of birth defects.