Q: I've had trouble getting pregnant and finally succeeded at the age of 37. Everyone says I should get an amniocentesis, but I'm afraid it will cause a miscarriage. What should I do?
A: First, let me address the so-called dangers of having an amniocentesis. In the past, doctors have told patients that there was a 0.5% pregnancy loss from this procedure. This was based on a quoted risk from the Centers for Disease Control and Prevention, who derived their statistics from three studies carried out in the 1970s in the U.S., Canada, and Great Britain.
Ultrasound monitoring with real time and upgrades in technology have probably made this procedure much safer. A recent analysis looked at amniocentesis loss rates in over 35,000 patients enrolled in the First and Second Trimester Evaluation of Risk for Aneuploidy (also known as FASTER). These women were pregnant with a single fetus and were followed from 10 and 13 weeks of gestation onwards. Over 3,000 of these women had an amniocentesis, whereas nearly 32,000 (the control group) did not. The researchers compared the rate of fetal loss that occurred up to 24 weeks of gestation in the two groups. The loss in the control group was 0.94 percent, whereas the loss in women with amniocentesis was 1.0 percent. This means that the difference was only 0.06 percent, which is not statistically significant.
Based on these updated numbers, amniocentesis is safe. This procedure will also allow for the most accurate determination of chromosomal abnormalities (such as Down syndrome) in the fetus. However, not every woman over 35 wants to or has to go through this procedure; there are other Down syndrome screening markers that can be obtained through tests that are noninvasive. Some of these can be done as early as the first trimester. These include ultrasound to check for nuchal translucency (an abnormal thickening in the area of the fetal neck that is present in this syndrome) and maternal blood tests for placental proteins and pregnancy markers, which are often abnormal in abnormal pregnancies. These combined tests have an 85 percent success rate in detecting Down syndrome.
The diagnosis will be enhanced if the tests are repeated in the second trimester (indeed some doctors wait until the second trimester to do these tests). There's a five percent false positive rate with noninvasive testing (i.e. the tests indicate there may be a fetal or pregnancy abnormality when none is present). Amniocentesis may be needed to rule out these false positives and obviously if amniocentesis is done in the first place, a false positive error will not occur.
Dr. Reichman's Bottom Line: Blood tests and an ultrasound will help you ascertain the true risk of your baby having Down syndrome, but an amniocentesis, if performed by an appropriately trained physician, is safe and will let you know the risk with greater certainty.
Dr. Judith Reichman, the “Today” show's medical contributor on women's health, has practiced obstetrics and gynecology for more than 20 years. You will find many answers to your questions in her latest book, "Slow Your Clock Down: The Complete Guide to a Healthy, Younger You," which is now available in paperback. It is published by William Morrow, a division of .
PLEASE NOTE: The information in this column should not be construed as providing specific medical advice, but rather to offer readers information to better understand their lives and health. It is not intended to provide an alternative to professional treatment or to replace the services of a physician.