A birth defect is any abnormality present at birth that results in physical or mental disability or death. The abnormality may affect the child’s structure, ability to function or metabolism. According to the Centers for Disease Control and Prevention (CDC), about 3 percent of infants born in the United States (about one in every 33 births each year) have some kind of birth defect. Furthermore, birth defects are the leading cause of death in the first year of life.

According to the American Academy of Family Physicians (AAFP), there are more than 4,000 different birth defects. They vary widely, from structural defects (e.g., heart defects, neural tube defects) to metabolic problems (e.g., phenylketonuria) and combinations of both. Many birth defects are genetic disorders caused by alterations to genes or chromosomes that affect normal development (e.g., Down syndrome, sickle cell anemia, cystic fibrosis).

Some birth defects are caused by a single, well-documented factor, such as a missing or abnormal gene or chromosome. Many are caused by a combination of several factors, such as maternal age, smoking, or medication use. Substances or infections that affect a pregnant woman may also affect the developing fetus and cause birth defects.

Many birth defects are defined by their cause, including fetal alcohol syndrome (due to maternal alcohol consumption) and congenital rubella syndrome (due to an infection with rubella in the first trimester). However, the causes of most birth defects are not known.

Birth defects are often detected before birth. Defects that have not been prenatally detected and are not obvious when the infant is born are usually discovered through newborn screening tests. While most birth defects are discovered in infancy, within the first year of life, some others may not be detected until childhood or even adulthood.

Some birth defects require little treatment. Other defects cannot be treated or will result in early death regardless of treatment attempts. However, most birth defects lie somewhere between these two extremes and are treatable to some degree.

Many birth defects are corrected through surgery in early infancy. Others can be treated through nonsurgical means. Birth defects that cause mental retardation and other developmental disabilities can present lifelong challenges to both parents and children. A few birth defects can be treated before birth using injections or even prenatal surgery.