Genetic Counseling
Lisa and Mark are expecting their first child. Both are healthy 30-somethings with no family history of birth defects. Still, they worry. "Should we see a genetic counselor?"
Modern genetics has identified 3,000 different birth defects that can occur in one in 29 births. Yet the risk of an individual couple like Lisa and Mark having a child with an abnormality depends on a variety of factors.
Birth defects result from genes alone or from environmental causes such as drug or alcohol abuse, infections, or exposure to medications or chemicals. Some result from a combination of heredity and environment. Certain diseases, like cystic fibrosis, are transmitted by a parent who is a "carrier", which means that the parent doesn't have the disease but carries a recessive gene that the child inherits. Some birth defects can be fatal, while others present lifelong challenges.
Genetic counseling provides information about human genetics based on family history and various tests. Ideally, couples may want to discuss genetic counseling before they conceive. In pre-conception counseling, a genetic counselor looks at the couple's state of health, the woman's age, whether she has diabetes or a seizure disorder, family history, and ethnicity. The counselor will also recommend that the woman begin taking vitamins containing folic acid three months prior to conception in order to prevent birth defects.
Genetic counseling is often advised for women older than 35 because chances of having a child with Down Syndrome increase with maternal age. If a woman has diabetes or a seizure disorder, she should discuss medications with her doctor before becoming pregnant.
Family history and ethnicity are important reasons to consider genetic counseling because some disorders occur more often in particular groups (e.g. Tay-Sachs in Jewish Europeans, thalassemia in Asians and Mediterraneans, sickle cell anemia in African Americans, and cystic fibrosis in Caucasians). Obtaining a family medical history enables care providers to consider the health of parents, their parents and grandparents.
Once she is pregnant, a woman is offered a "triple screen" test that can pick up abnormalities. This blood test is done between 14 and 22 weeks, and results are usually back in a week. This test "risk-sorts;" that is, it doesn't make a diagnosis but only suggests possibilities that require further testing — usually by ultrasound or amniocentesis.
Ultrasound is a non-invasive technique using sound waves to show an image of the uterus and fetus. It can measure, for example, thickness of the fetus's neck, which may indicate abnormality. Ultrasound can be done early, between nine and 14 weeks, or later if the triple screen picks up a risk factor. Many doctors offer a detailed ultrasound to look for birth defects to all pregnant women between 18 and 20 weeks. If an abnormality is detected, the woman may meet with a genetic counselor to consider genetic testing.
Women usually meet with a genetic counselor prior to having a genetic procedure such as amniocentesis or chorionic villus sampling (CVS). The counselor discusses the risks and benefits of the procedure with the woman.
In amniocentesis, a small amount of amniotic fluid is extracted through a needle inserted into the uterus. The sample, taken around 16 weeks, contains fetal cells that can be diagnosed. Results are usually back in seven to 14 days. The risks of infection or miscarriage are about one in 200.
CVS involves taking a sample of placental cells by inserting a needle through the mother's abdomen into the placenta or by inserting a slim tube through the vagina. It can be done earlier than amniocentesis - as early as the tenth week of pregnancy - but carries a slightly higher risk of miscarriage.
If a disease or defect is diagnosed, a couple will need to decide whether to terminate or continue the pregnancy. This is where a certified genetic counselor's input is critical. The counselor offers information about the fetus's chance of survival, medical problems that can occur, treatment options, and what the child's future is likely to hold in terms of physical, social, and mental challenges. The counselor will not try to influence the parents' personal decision.
Genetic counseling also informs parents about risks of having another child with an abnormality. In some cases, having one child with a genetic defect increases the likelihood that others may be affected. Counselors are also consulted by couples concerned about their risk of having a child with the same birth defect or genetic disease present in more distant relatives.
Whether it's a first pregnancy or a couple who already has a child with a birth defect, counseling can offer needed scientific information available to make these important decisions.
