Warning about prenatal test

Because of uncertainties about whether one type of prenatal test may increase the risk of fetal limb and facial abnormalities, FDA has required the manufacturer to add a warning about the risk to the test's patient labeling.

FDA is also requiring the test, called chorionic villus sampling (CVS), to carry revised physician instructions specifying that the test should only be done after the 10th week of pregnancy. Some research suggests this may reduce the risk.

CVS, like another prenatal test called amniocentesis, can detect genetic diseases such as Down syndrome, Tay-Sachs disease, and sickle cell anemia. The American College of Obstetricians and Gynecologists recommends prenatal testing for any woman who will be 35 or older when her baby is born. The college also recommends testing for any woman with a family history of genetic diseases.

With amniocentesis, a woman must wait until the 16th week of pregnancy before being tested, and the results can take 10 days or longer. In contrast, CVS can be performed earlier in the pregnancy, and the results are ready in a few days.

The risk of miscarriage is slightly higher for CVS, greater than 1.5 percent, compared to less than 1 percent for amniocentesis. According to FDA, it is not clear whether there is an increased risk of birth defects attributable to CVS and how large that risk is, if it exists.

A study conducted at Oxford University and published in the March 30, 1991, issue of The Lancet reported that, of 289 pregnancies with CVS testing, five babies had severe limb abnormalities and four of the five had facial deformities as well. Another study, conducted at the Humana Hospital-Michael Reese Medical Center in Chicago and published in the May 1992 issue of Obstetrics and Gynecology, reported four cases of limb deformities among 394 CVS-tested pregnancies. In the general population, these types of birth defects are rare, with estimates ranging from 1 in 2,000 births to as few as 1 in 175,000 births.

However, a letter in the June 8, 1991, issue of The Lancet reported that Yale University studies, which specifically addressed the safety of first-trimester CVS, did not show a significant increase among 9,588 pregnancies in these kinds of birth defects.

FDA has approved only one CVS testing device, the Trophocan CVS Catheter, manufactured by Concord/Portex, Inc., Keene, N.H., but several others are under clinical investigation. In addition to the patient warning on the approved test, the agency is requiring that the same warning about possible birth defects be included in the informed consent for the investigational devices. The protocol for these investigations must also specify that the test can't be conducted until after the 1Oth week of pregnancy.

FDA is also requiring that clinical investigators immediately report any limb or facial defects in newborns whose mothers underwent CVS. (For more information on prenatal tests, see "Genetic Screening-Fetal Signposts on a Journey of Discovery" in the December 1990 FDA Consumer.)

Share this with your friends