Prenatal Diagnostics Found to Pose Low Risk

A new study has found that pregnant women undergoing prenatal diagnostic testing to identify genetic or chromosomal abnormalities have a lower risk of miscarriage than previously believed.

Amniocentesis and chorionic villus sampling (CVS) are common prenatal tests performed during the first and second trimester of pregnancy. CVS testing has been thought to have a higher rate of miscarriage than amniocentesis. However, the results of a 20-year retrospective comparison study reported in the September 2006 issue of Obstetrics and Gynecology have shown this not to be so. The study looked at data from 9,886 CVS and 30,893 amniocentesis procedures. When the researchers controlled for gestational age and maternal age, they found there were no differences between the losses from CVS or amniocentesis.

"We saw that the rate of miscarriage risk attributable to CVS had declined over time,” said study co-author Mary E. Norton, M.D., medical director of the Prenatal Diagnostic Clinic at the University of California, San Francisco (USA). "One possible reason is that over time, practitioners have become more proficient in performing CVS procedures.”

While amniocentesis requires insertion of a hollow needle through the abdominal wall and into the uterus to withdraw amniotic fluid, CVS involves removing a piece of tissue from the placenta. In both cases, the samples are then cultured and the chromosomes are analyzed to determine abnormalities associated with Down syndrome and other genetic diseases, such as cystic fibrosis and sickle cell disease. CVS can be performed at an earlier gestation period (10-12 weeks) than amniocentesis (16-20 weeks), and is therefore preferred by some patients because of the earlier detection of possible abnormalities.

More recent studies have shown that tests such as a specialized ultrasound of the fetal neck, known as nuchal translucency ultrasound, combined with early blood screening have a better detection rate and can be completed much earlier in the pregnancy.



Related Links:
University of California, San Francisco