Congenital Anomalies

Question: What are examples of congenital anomalies?

Congenital anomalies include bone disorders, cataract, cleft palate, cretinism, Down's syndrome, congenital heart disease, hemophilia, joint disorders, pyloric stenosis, and spina bifida. Blindness, deafness, hydrocephalus, and jaundice are also often due to congenital anomalies, although in other cases they are the result of event that occurred after birth.

Limbs or organs may be malformed, duplicated, or entirely absent. Organs may fail to move to the correct place, as in cryptorchidism; fail to open correctly as in imperforate anus; or fail to close at the correct time, as in patent ductus arteriosus. Congenital anomalies often occur together. For example, 33 percent of babies born with Down's syndrome also have heart disease.

Question: What may cause the development of congenital anomalies?

Congenital anomalies arise from the faulty development of a fetus, caused either by genetic disorders or other factors. Some anomalies arise from a combination of factors, and the underlying cause is far from clear in all cases.

Question: How are genetic disorders responsible for congenital anomalies?

Inherited congenital anomalies generally result from the presence of abnormal genes or chromosomes. Heredity is determined by corresponding pairs of genes, called alleles. One of these paired genes is dominant and the other recessive, and it is the dominant gene that governs the transmitted trait or characteristic. Thus, if the abnormal gene of a pair is dominant, the abnormal or anomalous trait will be conveyed to the embryo. If the abnormal gene is recessive, then both genes in the pair have to be abnormal for a congenital anomaly to occur.

Some congenital anomalies, such as hemophilia, are linked to a defect of one of the sex chromosomes. Many genetic disorders, however, are neither wholly dominant, recessive, nor sex-linked, but may be caused by more than one abnormal pair of genes.

Question: What other factors may cause congenital anomalies?

Infection in the mother is a common cause of abnormality in a baby. For example, an attack of rubella during the first three months of pregnanacy may cause her child to be born deaf or have cataracts, heart disease, jaundice, or other anomalies. Cytomegalovirus (CMV) and toxoplasmosis also cause congenital anomalies.

Certain drugs taken by a woman during pregnancy are often responsible for abnormalities in the child. For example, large doses of corticosteroids can cause a variety of congenital defects, as can some anticonvulsants given to control epilepsy. Other drugs include anticancer drugs; narcotics and sedatives; tranquilizers and antidepressants; antibacterials, especially tetracycline; anticoagulants; drugs prescribed to treat cardiac conditions and hypertension; oral hypoglycemic used to treat diabetes in the mother; and, of course, heavy consumption of alcohol. Other drugs may cause gross abnormalities, such as the defects arising from thalidomide. A pregnant woman should, thus, avoid taking any medication without first consulting with her physician.

Injury to a pregnant woman or to a fetus is another cause of congenital anomalies. For example, limbs may be malformed if an intrauterine device (IUD) is not removed early in the pregnancy. Smoking during pregnancy is implicated as one factor in the incidence of abnormally low birth weight in babies, and malnutrition seems to be related to a high incidence of congenital anomalies. The age of the woman at the time she conceives can also be a factor. For example, Down's syndrome occurs more frequently when conception occurs after the age of about 35.

Congenital anomalies have also been attributed to the effects of X-ray examination made early in a pregnancy.

Question: Is it possible to diagnose congenital anomalies in a fetus?

Yes. The most reliable method of diagnosis is to examine a sample of fluid from the amniotic sac, sometime between the fifteenth and eighteenth week of pregnancy. The sample is obtained by amniocentesis. Microscopic examination of the cells in the fluid then reveals possible abnormalities in the chromosomes. Congenital anomalies that can be diagnosed in this way include Down's syndrome, spina bifida, and anencephaly. Sometimes, the diagnostic use of ultrasound can detect abnormalities of the skull or spine.

Question: Can congenital anomalies be treated?

Treatment depends entirely on the nature and severity of the condition. Many anomalies can be treated, but for some there is no treatment.

Question: In what circumstances might abortion be considered?

Abortion might be considered if serious fetal disorders are found early in a pregnancy. The decision to abort rests with the parents and is made after considering the advice of the physician and specialists on the nature of the disorder and the consequences of abortion.

Question: Are congenital anomalies more likely to occur in first-born babies?

No. Statistics disprove this commonly held belief.

Question: Does a congenital anomaly in a baby indicate that subsequent babies will be similarly affected?

Genetic counseling deals with such questions. In many cases it is possible to state risks numerically. For example, a baby with congenital heart disease is likely to be followed by a similarly affected child in 2 percent of pregnancies instead of the ordinary risk of one percent. Spina bifida occurs in about 1 child in every 1,500, but if a previous child was born with the condition, there is about a 1-in-20 to 1-in-50 chance that it will occur in a later child.