When CVS was introduced to the United States, in the mid-1980s, doctors and patients welcomed it as an important tool to diagnose genetic defects as early as the ninth week of pregnancy. Although amniocentesis, a more established prenatal screening test, had been available since the early 1970s, it usually couldn’t be done until the 16th week. For mothers in their 30s and 40s, who are at greater risk of bearing children with genetic abnormalities, CVS provided much-needed answers much more quickly. Some 80,000 procedures have been done worldwide. Now CVS is the subject of a medical debate: two controversial recent studies suggest it could be linked to the kind of serious congenital deformities little Sarah Kernatz has.
The new studies contradict evidence of thousands of cases showing that CVS is safe when performed by experienced physicians. But Chicago’s Humana Hospital-Michael Reese, where one of the studies was conducted, was concerned enough to stop offering the procedure. At Brigham and Women’s Hospital in Boston, chief of obstretrics Dr. Fredric Frigoletto has halted all but a few CVS procedures. At the Hospital of the University of Pennsylvania in Philadelphia and Columbia-Presbyterian Hospital in New York, counselors advise patients seeking CVS of the possibility of birth defects. And this month the National Institutes of Health will recommend that all hospitals and clinics tell women considering CVS about the reports. “We feel we should provide the information [for] informed consent,” says the NIH’s Dr. Felix de la Cruz. “I think it is a personal choice.”
CVS and amniocentesis are recommended most often for women over 35 or those who have a family history of specific genetic diseases. In amniocentesis, cells drawn from the amniotic fluid are cultured and analyzed for the presence of chromosomal abnormalities like Down syndrome, as well as severe malformations of the developing spinal cord like spina bifida and anencephaly. Because culturing and analyzing the cells can take until the 20th week of pregnancy, women who decide to abort an abnormal fetus add some medical risk to their sorrow.
CVS is a somewhat trickier procedure. The doctor inserts a flexible catheter through the vagina and cervix to suck out a tiny piece of tissue from the chorionic villi, the threadlike projections on the outermost layer of the amniotic sac. CVS can detect chromosomal defects, and identifies a number of diseases much earlier than amnio can, including TaySachs, sickle cell anemia, cystic fibrosis and Duchenne muscular dystrophy.
In one of the troubling new CVS studies, Dr. Barbara Burton of Humana-Michael Reese found four cases of limb deformities in 394 women who had CVS in the ninth and 10th weeks of pregnancy. A similar study from Oxford University, published last year, reported five such anomalies out of 289 births. In the general population, the incidence of such defects–which include missing, shortened or stublike fingers and toes–is much less common: about one in 2,000 births.
In a much larger 1991 study, CVS pioneer Dr. Laird Jackson of Philadelphia’s Jefferson Medical College and Dr. Bruno Brambati of Milan found only five cases of limb deformities in more than 12,000 women. “CVS has been performed tens of thousands of times around the world,” says Dr. Eugene Pergament, who is head of reproductive genetics at Northwestern University Prentice Women’s Hospital in Chicago. If the rate of limb defects was as high as the Humana-Michael Reese team found, he believes, “it would have been observed much earlier and in many different places.” A spokesman for Humana-Michael Reese would not comment on the study or the criticism it has received because the research took place before Humana Inc. acquired the hospital.
Earlier studies had also linked CVS to an increase in miscarriages. Some research indicates that spontaneous abortion occurs in about 2 percent of women who have CVS-more than twice the rate associated with amniocentesis. But since most miscarriages occur in the first trimester anyway, it’s hard to tell if they are related to CVS.
A good success rate with CVS depends on the skill and experience of the practitioner, says Dr. John Williams, medical director of the Prenatal Diagnostic Center of Southern California, who has performed more than 4,000 of the procedures since 1985. “There’s a learning curve,” he says. “It took me until I’d done about 400 cases before I really became proficient.” (Doctors hone their CVS skills in part by practicing on women scheduled for abortions.) In the Chicago study, all procedures were performed by a single perinatologist who had previously done 150 CVS screenings, or by an assistant under his supervision. Under-trained practitioners, Williams says, could cause trauma to the placenta, which could disrupt normal fetal development.
Toni Mann, a travel coordinator from West Hollywood, Calif., will be 35 when her baby is born in November. She chose to have CVS last month, in her 11th week of pregnancy, and learned the result’s the following week. Her baby is normal. “I felt that knowing in advance was worth taking that possible extra risk,” she says. “It would be very difficult for me to terminate a pregnancy after waiting for an amnio–you’re 18 weeks pregnant, you’re feeling life and you’re already showing.”
Other women considering CVS find it a difficult decision. Most genetics experts believe the test does not cause birth defects, but to minimize any possible risk, it’s important to choose a facility that has broad experience with the technique– even if it means traveling to another city. When early diagnosis of a genetic abnormality is a woman’s first concern, CVS can provide peace of mind.
In the future, prenatal screening for genetic defects may be no more threatening than taking a blood sample from a pregnant woman’s arm. At Boston’s Children’s Hospital, genetics researcher Dr. Diana Bianchi has devised a technique for capturing fetal cells that leak through the placenta into the mother’s bloodstream. So far, she has screened several hundred pregnant women, but says thousands will be needed to evaluate her test’s accuracy. Her work is three to five years away from clinical trials. For Bianchi and other researchers, the goal is simple but ambitious: to find a way to probe the secrets of the developing fetus without invading the peace and protection of the womb.
Tough Choices for Women at Risk
These two prenatal screening tests provide similar information about the developing fetus at different stages of gestation; they’re especially important for older mothers.
A flexible catheter, inserted vaginally, is guided by ultrasound along the uterine walls. Suction allows the catheter to extract fetal cells from the threadlike projections (villi) on the chorion, the outermost embryonic layer.
A hollow needle, inserted through the mother’s abdomen, extracts a sample of the amniotic fluid surrounding the embryo.
