NEW YORK - Amniocentesis performed during the fourth through sixth month of pregnancy, known as the "midtrimester," does not increase the rate of miscarriage, according to a report in the journal Obstetrics & Gynecology.

Amniocentesis involves the insertion of a needle into the mother's abdomen and then into the uterus to obtain a sample of the amniotic fluid that surrounds the developing baby. This fluid can be analyzed to determine the presence of chromosome disorders, such as Down's syndrome, as well as the sex of the baby.

Although the pregnancy loss rate attributed to midtrimester amniocentesis is usually quoted as just 0.5 percent, the authors point out, many doctors still consider this to be an overestimate.

To investigate further, Dr. Keith A. Eddleman from Mount Sinai School of Medicine, New York and colleagues used a large database to estimate the pregnancy loss rate after midtrimester amniocentesis. About 3,000 women who underwent amniocentesis were compared with more than 31,000 who did not.

Pregnancy loss was rare in women who underwent amniocentesis and the rate was comparable to that seen in women who did not have the procedure, suggesting that amniocentesis itself really didn't raise the risk of pregnancy loss.

In fact, among women older than 35 years old, the loss rate after amniocentesis (1.06 percent) was actually lower than the loss rate for women who did not undergo amniocentesis (1.92 percent), the researchers note.

Eddleman told Reuters Health that "we need to move away from the concept of using age alone to determine who should be offered amniocentesis."

Overall, the researchers conclude that "this study provides the best possible contemporary information about procedure-related loss rates after amniocentesis and calls into question the relevance of commonly quoted higher loss-rates from older studies."

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