Amniocentesis & Miscarriage Risk

Amniocentesis & Miscarriage Risk

With my first two children, I had normal pregnancies. In my third pregnancy, since I was over 35, we had an amniocentesis. The procedure went "flawlessly," and two weeks later we learned we could expect a "genetically perfect" baby girl. Three days after that, my water broke and I miscarried. My doctor could not tell me why, but he discounted that the amnio was the cause. That was five months ago. Now I am six weeks pregnant. My husband insists that I have another amnio because I will be 38 at delivery. I am worried about another miscarriage. Can an amnio cause a miscarriage more than two weeks after the procedure is performed? Is there an alternative to amnio that poses less risk? Mary

There is a risk of ruptured membranes and pregnancy loss after an amniocentesis. However, this risk is small, and your chance of miscarriage should not be increased this time just because you had a complication that occurred after a previous amniocentesis.

Amniocentesis is commonly performed to check for genetic abnormalities such as Down syndrome. The risk of this genetic condition increases as a woman ages. At age 35, the risk is about one of every 200 pregnancies, while at age 40, the risk rises to as much as one of every 50 to 100 pregnancies. Amniocentesis is performed using an ultrasound examination to pinpoint a pocket of fluid inside the uterus. The physician guides a needle through the abdomen into the pocket and removes some fluid. The fluid is sent for cell culture. After a few days, fetal cells from the culture are analyzed for their chromosomal makeup.

A faster method of analysis, called FISH for "fluorescent in situ hybridization," involves using special dyes targeted to specific chromosomes. Each dye glows a different color under fluorescent lighting. At present, we can only test for four or five different chromosome pairs using this technique. Normal cells have 23 pairs of chromosomes; an abnormal fetus may have an extra chromosome or may be missing one from a pair. Since we can't test all the chromosome pairs using FISH, this method only picks up a portion of the potential chromosomal anomalies that may occur. Luckily, the most common problems are picked up using this screening method. As results from this test can be available within a few hours, FISH is gaining in popularity. A major concern with amniocentesis is that it needs to be performed well into the second trimester of pregnancy. The wait can be quite stressful, and if the test suggests that the fetus is abnormal, the couple faces difficult decisions at a point fairly far along in the pregnancy.

An alternative method, called chorionic villus sampling (CVS), can provide results much earlier, near the end of the first trimester. Using ultrasound guidance, a catheter is placed through the cervix and into the uterus to a spot just below the placenta. A small biopsy is removed by suction and sent for evaluation. Again, both FISH and cell culture and chromosomal analysis can be used. Unfortunately, CVS has a miscarriage rate that is slightly higher than amniocentesis.

I would suggest you meet with a perinatologist who can discuss your concerns regarding potential risks and advise you appropriately.

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