Gene Screen

Early fetal checkup

For Donna and Steven Roehl and Debbie and Maury Fisher, having a baby is a risky business. The Roehls both carry the gene for Niemann-Pick disease, a metabolic disorder that has already taken the life of their first child. The Fishers are carriers of Tay-Sachs disease, a fatal ailment that afflicts their two-year-old son. For both couples, the odds are one in four that any child they bear will be defective. When the two wives became pregnant earlier this year, they intended to undergo amniocentesis, a test to determine if the fetuses were normal. Each planned to abort if it was not.

But amniocentesis usually cannot be done until the 16th or 17th week of pregnancy, when there is enough amniotic fluid to obtain a sample safely via a needle through the abdomen. Results are not available for another four weeks. Eager to avoid five months of anxious waiting, the two women volunteered for a new, early test of fetal health, under study at Michael Reese Hospital in Chicago. Fisher had the procedure in her ninth week "and found out the next day that my baby did not have Tay-Sachs." Roehl also got good news, fast.

The test, called chorionic villi sampling (CVS), is a painless procedure and can be done in a physician's office as early as the fifth week of pregnancy. To perform it, the obstetrician inserts a long thin tube through the vagina into the uterus. A second doctor, following the procedure on an ultrasound monitor, helps the obstetrician position the catheter between the lining of the uterus and the chorion, a layer of tissue that surrounds the embryo during the first two months and later develops into the placenta. The goal is to suction up a sample of the chorionic villi, finger-like projections of tissue that transfer oxygen, nutrients and waste between mother and embryo. "It's like vacuuming a shag rug; you get about half a dozen villi," explains Dr. Laird Jackson of Philadelphia's Jefferson Medical College, which has helped pioneer the technique in the U.S. Since the tiny chorion sample is composed of the same cells as the fetus, genetic defects present in the child should show up in laboratory analysis.

Dr. Eugene Pergament of Michael Reese is convinced that CVS "will eventually replace amniocentesis as the first line of genetic diagnosis." Earlier detection not only means less anxiety for the mother, it also means that should she choose to terminate the pregnancy, she can have a simple outpatient abortion after six to eight weeks rather than a far more complex one at five months, requiring hospitalization. "And no matter how you feel about abortion," says Jackson, "there is a difference in our perception of pregnancy at eight weeks and at 20."

The cost of cvs, which will soon be available at some 35 hospitals, is $550 to $800, about the same as amniocentesis. The risks, though not fully known, are probably also the same: one in 200 women who have undergone amniocentesis suffers complications (infection, for example) that may lead to miscarriage. For this reason the new test will be recommended only for women known to have a high risk of delivering an abnormal baby, including the growing number who wait until age 35 or later to have their first child. CVS may some day prove to be valuable for another reason, says Dorothy Davis, spokesperson for the March of Dimes. Early detection of genetic defects may make it possible for doctors to intervene and correct problems while the child is in the womb. - This file is automatically generated by a robot program, so viewer discretion is required.