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Aug. 30, 2006 — The risk of pregnancy loss (miscarriage) after undergoing chorionic villus sampling (CVS) to detect birth defects is lower than previously thought and essentially carries no higher a risk than the more commonly used amniocentesis procedure, according to new research published in the September issue of Obstetrics & Gynecology. While both procedures carry a small risk of causing miscarriage, this study found that the miscarriage risk attributable to CVS is the same as the risk of one in 370 seen with amniocentesis when adjusting for the earlier gestational age of the CVS procedure. These findings are important because most women prefer prenatal screening as early as possible in pregnancy, and CVS is performed earlier than amniocentesis.
Amniocentesis is an invasive diagnostic procedure used to detect certain birth defects and is performed early in the second trimester (16 to 20 weeks gestation). Amniocentesis involves inserting a needle through the abdomen into the uterus to collect a small sample of amniotic fluid for testing of chromosomal abnormalities in the fetus. CVS also is an invasive procedure used to detect certain birth defects but is done in the first trimester (10 to 12 weeks gestation). CVS collects a small sample of chorionic villi (tiny parts of the placenta) cells from the lining of the uterus either by inserting a slender needle through the abdomen into the placenta or by inserting a very thin plastic tube into the vagina, through the cervix and into the placenta.
Researchers at the University of California, San Francisco, studied data from 1983 to 2003 on all CVS and amniocentesis procedures (9,886 and 30,893, respectively) performed at a single prenatal diagnostic center. The researchers compared pregnancy loss rates for both procedures and studied whether the pregnancy loss rate between the two procedures had changed during the past 20 years.
Based on earlier research, women have been counseled that the miscarriage risk from CVS is greater than with amniocentesis. This study found that the overall pregnancy loss rate over the 20-year period for CVS was 3.12 percent and 0.83 percent for amniocentesis. However, when examined in five-year intervals, the pregnancy loss rate from CVS dropped significantly in the last five-year period of the study (1998-2003), down to 1.93 percent. When the researchers controlled for gestational age, maternal age, and indication for the procedure, they found no difference between losses from CVS or amniocentesis. The researchers caution that these findings are on a relatively small cohort of women from a single institution. Further, they suggest that one possible cause of the decrease in pregnancy loss rate from CVS may be due to increased proficiency with the procedure by specialists. According to the researchers, these findings are important for physicians and their patients. Women deciding whether to undergo CVS or amniocentesis can use this information to decide whether they want first-trimester testing or second-trimester testing.
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