Congenital abnormalities are caused by problems during the fetus’s development before birth. Thanks to improved medical care during pregnancy and to progress in early detection of chromosomal and other genetic abnormalities through amniocentesis, chorionic villus sampling, and other newer diagnostic tests, there are fewer and fewer newborns with congenital problems. About three of every hundred babies born in the United States have congenital abnormalities that will affect the way they look, develop, or function—in some cases for the rest of their lives.
There are five categories of these abnormalities, grouped according to the cause.
Chromosomes are the structures that carry the genetic material inherited from one generation to the next. Normally, twenty-three chromosomes come from the father and twenty-three from the mother, and all are found in the center of every cell in the body except the red blood cells. The genes carried on the chromosomes determine how the baby will grow, what she will look like, and to a certain extent how she will function.
When a child does not have the normal forty-six chromosomes, or when pieces of the chromosomes are missing or duplicated, she may look and behave differently from others her age, and she may develop serious health problems, as well. Down syndrome is an example of a condition that can occur when a child is born with an extra chromosome.
Sometimes the chromosomes are normal in number, but one or more of the genes on them are abnormal. Some of these genetic abnormalities can be passed on to the child if one of the parents is affected with the same abnormality. This is known as autosomal dominant inheritance.
Other genetic problems can be passed to the child only if both parents carry the same defective gene. (Cystic fibrosis, Tay-Sachs disease, and sickle cell anemia are all examples of this type of abnormality.) In these cases both parents are normal, but one in four of their children would be expected to be affected. This is known as autosomal recessive inheritance.
A third type of genetic abnormality is called sex-linked, and generally is passed on to boys only. Girls may carry the abnormal gene that causes these disorders but not show the actual disease. (Examples of this problem include hemophilia, color blindness, and the common forms of muscular dystrophy.)
Conditions During Pregnancy That Affect The Baby
Certain illnesses during pregnancy, particularly during the first nine weeks, can cause serious congenital abnormalities—German measles and diabetes, for example. Alcohol consumption and certain drugs during pregnancy significantly increase the risk that a baby will be born with abnormalities.
Certain medications, if taken during pregnancy, also can cause permanent damage to the fetus, as can certain chemicals that can pollute air, water, and food. Always check with your doctor before using any medication or supplement while you are pregnant.
Combination of Genetic and Environmental Problems
Spina bifida and cleft lip and palate are types of congenital abnormalities that may occur when there is a genetic tendency for the condition combined with exposure to certain environmental influences within the womb during critical stages of the pregnancy.
The vast majority of congenital abnormalities have no known cause. This situation is particularly troubling for parents who plan to have more children, because there is no way to predict if the problem will recur. If you and your family have experienced such a genetic-related birth abnormality, ask your pediatrician for a referral to a genetic counseling service. These services have expertise with a variety of genetic abnormalities and may be able to advise you as to the proper course of action.