Women should weigh benefits of prenatal testing against potential risks, costs

WOMEN'S HEALTH

June 21, 1994|By Dr. Genevieve Matanoski | Dr. Genevieve Matanoski,Medical Tribune News Service

In the past several decades, medical science has developed new ways to monitor the health and development of fetuses. It now is possible to detect disease, defects and other genetic disorders in the womb, a feat not possible a generation ago. These modern procedures give both the physician and the pregnant woman a literal insight into the health of the developing fetus.

As with any medical procedure, prenatal testing is most effective when women have a clear, informed understanding of its purposes, benefits, risks and costs. To find the answers to my questions, I consulted Virginia Corson, a genetic counselor in the Prenatal Diagnostic Center of the Johns Hopkins Hospital.

Q: Who should have prenatal testing?

A: Although prenatal testing is available to all women, there are selected groups of women for whom it is especially important.

One such group is women in their mid-30s or older, whose children are at increased risk of certain chromosomal abnormalities such as Down Syndrome. Another group is women whose families have a history of genetic disorders, such as muscular dystrophy, cystic fibrosis and hemophilia. Women who have had a previous child with a genetic disorder such as Down Syndrome also are advised to be tested. Based on the results of a blood-screening test or sonogram, other women also may have testing recommended to them.

Q: What tests are available? How do they work and what do they reveal?

A: Prenatal tests include sonography, amniocentesis and chorionic villus sampling (CVS).

Sonography (sometimes referred to as ultrasound), a noninvasive procedure, uses ultrasound waves reflected off tissue to study the womb, placenta and fetus. This procedure indicates where the placenta is located, the status of fetal development and how far the pregnancy has progressed. Certain major defects also are detectable by sonography. A sonogram can be done about 16 to 18 weeks into the pregnancy, and/or throughout the course of pregnancy, to check fetal organ development.

Amniocentesis involves placement of a needle into the womb to collect less than 2 tablespoons of amniotic fluid, the fluid surrounding the fetus. This fluid contains cells, which can be grown and harvested, that have been shed by the fetus. The chromosomes from these fetal cells can be studied to determine if they are normal.

In some patients, studies to rule out other genetic problems will be indicated. A small portion of the amniotic fluid can be measured for a substance called alpha-fetoprotein (AFP), a protein made by the fetus. An elevated AFP value can signal certain conditions, particularly structural abnormalities involving the spinal column and brain.

Since the amniotic-fluid cells take time to grow, test results usually are only available within two to three weeks. Amniocentesis usually is performed 15 to 17 weeks into the pregnancy.

Chorionic villus sampling (CVS) is a new alternative to amniocentesis. Tiny samples of the developing placenta are obtained through the vagina or abdomen. In the vaginal method, a catheter is advanced through the cervix to the placenta. Minimal discomfort is associated with the procedure, which takes just a few minutes to perform. If the placenta is more accessible through the abdomen, the procedure is carried out through the abdominal wall in a way similar to amniocentesis.

CVS is performed about 10 to 11 weeks from the beginning of the last normal menstrual period. As with amniotic-fluid cells, chorionic villi can be grown in the laboratory, and appropriate chromosome and/or biochemical tests then are performed. Results are available within two to three weeks.

Q: What are the risks involved?

A: There are no known risks to the fetus from ultrasound. Amniocentesis and CVS generally are considered safe, although both procedures carry a small risk of miscarriage. Since the tests are invasive, there is a chance of disturbance to the womb membrane or placenta, or of infection.

What each woman must do is weigh the risks, however slight, against the benefits. Remember that this is elective testing. The purpose of genetic counseling is to try to furnish full information, to help each woman make an informed choice.

Q: Are these tests usually covered by insurance?

A: Often, medical insurance will cover a portion or all of the costs associated with these tests. HMOs in particular often cover these charges. Consult your health-insurance coverage and your physician when making arrangements for testing.

Dr. Matanoski is a physician and epidemiologist at the Johns Hopkins School of Hygiene and Public Health. She is a founding director of the school's Institute for Women's Health Research and Policy.

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