Amniocentesis doesn't increase risk of pregnancy loss

January 1, 2007

Midtrimester amniocentesis causes fatal complications in only six out of 10,000 fetuses (0.06%), not five out of 1,000 (0.5%), the oft-quoted CDC statistic, according to a new study.

Midtrimester amniocentesis causes fatal complications in only six out of 10,000 fetuses (0.06%), not five out of 1,000 (0.5%), the oft-quoted CDC statistic, according to a new study.

The new figure is based on a prospective study of 35,000 unselected women with viable singleton pregnancies enrolled in the First and Second Trimester Evaluation of Risk for Aneuploidy trial and is not significantly different from the rate of fetal loss among women not undergoing the procedure. In the study, the rate of spontaneous fetal loss at less than 24 weeks' gestation in the study group was 1.0% and in the control group was 0.94% (P=0.74). In other words, women receiving the procedure were 1.1 times as likely to have a spontaneous loss as women not undergoing the procedure.

According to the authors of the new study, the old, traditionally quoted figure was derived from three nationally sponsored unrandomized studies in the US, Canada, and Great Britain performed in the 1970s when ultrasound was not routine and was drastically inferior in quality to that available today. Also, according to the authors, routinely offering amniocentesis to every woman over the age of 35 is "arbitrary and archaic" and "should be abandoned for a more customized risk assessment."

Commentary from Sharon T. Phelan, MD, Professor, Department of Obstetrics and Gynecology, University of New Mexico, Albuquerque, N.M.:

Most obstetricians have always suspected that in experienced hands the often quoted loss rate of 0.5% was excessive; but it did make the recommendation of genetic screening at age 35 more sensible. This lower risk determination potentially opens up the ability to offer genetic screening to younger women. However, just because a test can be done does not mean it should be done. There needs to be an indication or a specific question to answer, not simply "Is my baby normal?" Patients also need to understand that genetic amniocentesis is not a guarantee that they will have a normal, perfect Gerber's baby.