Amniocentesis is the most commonly prescribed invasive test performed during pregnancies in the United States. Most women fear them while doctors recommend them based on guidelines from the American College of Obstetricians and Gynecologists. These guidelines stem from past research studies and recommendations by the CDC that were based only on maternal age. Studies that are decades old have suggested that amniocentesis increases the rate of miscarriage by 0.5% or 1 in 200 pregnancies. However, researchers at Mount School of Medicine in conjunction with other institutions involved in the First and Second Trimester Evaluation of Risk for Aneuploidy trial (FASTER trial) have just reported in the November issue of the journal Obstetrics & Gynecology, that pregnancy miscarriage rates after routine midtrimester amniocentesis are significantly lower than rates previously published years ago in the 1970s and 1980s. This study reports that the amniocentesis procedure- related loss risk is approximately 1 in 1,600 pregnancies.
Lead author of the study, “Pregnancy Loss Rates After Midtrimester Amniocentis”, Dr. Keith E. Eddleman, MD, Associate Professor of Obstetrics, Gynecology and Reproductive Sciences at Mount Sinai School of Medicine has found that this new study now refutes the typically quoted 0.5% pregnancy loss rate and suggests it may be even lower than 0.1%.”Women should be counseled that this older loss rate is archaic and their decision about whether or not to have an amniocentesis should be based on contemporary information about miscarriage rates with newer screening techniques, rather than just relying on general age based risks,” said Eddleman. “This new research breakthrough will have a significant effect on how women are counseled about amniocentesis by their doctors and the information they have when deciding about screening for their unborn child.”
One of the purposes of the FASTER trial was to calculate the contemporary procedure-related loss rate after midtrimester amniocentesis using patients who were recruited for aneuploidy screening. A total of 35,003 unselected patients were enrolled between 10 3/7 and 13 6/7 weeks of pregnancy and followed until the end of pregnancy. Two groups were derived- those who did or did not undergo amniocentesis. The rate of fetal loss was compared between these groups and the fetal loss rate less than 6 months of gestation was 1.0% and was not statistically different from the control group.
According to researchers, the procedure related loss rate after amniocentesis was 0.06%. Women undergoing amniocentesis were only 1.1 times more likely to have a spontaneous loss. Researchers concluded that the procedure related loss rate after midtrimester amniocentesis performed on patients in a contemporary clinical trial was 0.06%. There was no significant difference in loss rates between those undergoing amniocentesis and those not undergoing amniocentesis.
Aneuploidy is a chromosomal imbalance of one or a few chromosomes above or below the normal human chromosomal number of 46, which may lead a child to have abnormalities including Down Syndrome. Amniocentesis is the standard prenatal detection procedure for aneuploidy. It has been a standard clinical practice to test women using this procedure who are 35 years or older as well as women who are genetically predisposed for certain disorders.