Prenatal test safer than once thought

The risk of miscarriage after undergoing chorionic villus sampling, or CVS, to detect birth defects is lower than previously thought and essentially carries the same risk as the more commonly used amniocentesis, according to new research.

The findings, although based on a fairly small sample of cases, are important because most women prefer prenatal screening as early as possible in pregnancy.

Amniocentesis, which involves inserting a needle through the abdomen into the uterus to withdraw amniotic fluid, is performed early in the second trimester at 16 to 20 weeks of pregnancy.

CVS involves collecting a small sample of placenta cells from the lining of the uterus either by inserting a slender needle through the abdomen or by inserting a thin plastic tube through the vagina into the placenta. It is done in the first trimester, between 10 and 12 weeks gestation.

Researchers at UC San Francisco studied data from 1983 to 2003 on nearly 10,000 CVS and 31,000 amniocentesis procedures performed at a single prenatal diagnostic center.

The study, published in the September issue of the journal Obstetrics & Gynecology, found that the overall pregnancy loss rate over the 20-year period was 3.12% for CVS and 0.83% for amniocentesis.

When the researchers controlled for gestational age, maternal age and indication for the procedure, they found no difference between losses from CVS or amniocentesis.

And, when examined in five-year intervals, the pregnancy loss rate from CVS dropped to 1.93% in the last five-year period of the study.

They suggested that the miscarriage rate from CVS may have decreased as doctors became increasingly proficient at performing the procedure.