Two standard tests - amniocentesis and chorionic villus sampling (CVS) - are common prenatal tests performed during the first and second trimester of pregnancy. Early testing using the CVS procedure has typically been thought to have a higher rate of miscarriage than amniocentesis. However, in a 20-year retrospective comparison study of the two procedures, researchers found that the loss rates for both procedures decreased over time.
"This is a significant finding for use as information in both patient counselling and in establishing widespread prenatal diagnostic and screening programs," said study co-author Mary E. Norton, MD, who is medical director of the Prenatal Diagnostic Center at University of California, San Francisco (UCSF) Medical Center and associate clinical professor in the UCSF Department of Obstetrics, Gynecology and Reproductive Sciences.
CVS can be performed at an earlier gestation period (10-12 weeks) than amniocentesis (16-20 weeks), and therefore is preferred by some patients because of earlier detection of possible abnormalities, according to Norton.
The study looked at data from 9,886 CVS and 30,893 amniocentesis procedures performed at UCSF Medical Center from 1983 to 2003. Overall, the pregnancy loss rate for patients undergoing CVS was greater (3.12 percent) than that of amniocentesis (0.83 percent). However, when examining the data at five-year intervals, the difference between the two procedures coincided with the highest occurring from 1983 through 1987 and lowest from 1998 through 2003.
"We saw that the rate of miscarriage risk attributable to CVS had declined over time," said Norton. "One possible reason is that over time practitioners have become more proficient in performing CVS procedures."
MEDICA.de; Source: University of California - San Francisco