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Rate of Miscarriage With Amniocentesis

Amniocentesis, the removal of fluid from around your baby while in the womb, is typically performed to check for genetic abnormalities, especially if you're older than 35 or if an earlier screening test reveals a possible birth defect. As with any invasive medical procedure, undergoing this procedure is not without risk.

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How It's Performed

Typically, amniocentesis is performed after the 15th week of pregnancy with the woman treated as an outpatient, the Mayo Clinic notes. There are two different types of amniocentesis tests.

Genetic amniocentesis tests for chromosomal abnormalities, such as those that can cause Down's syndrome or Trisomy 18, while maturity amniocentesis checks to make sure the baby's lungs are ready for delivery, especially if the mother must give birth early.

The doctor will perform an ultrasound first to determine your baby's exact location, and then, after prepping the area with an antiseptic, will insert a long, thin needed through your abdomen into your uterus. The fluid is collected into a syringe for testing. Following the procedure, you may feel cramping or experience a small amount of vaginal bleeding. The procedure is relatively quick and is typically completed within 30 minutes. Your physician may keep you longer to monitor your baby's heart rate following the test.

A Low-Risk Procedure

The risk of miscarriage following amniocentesis is quite low and variable – approximately 1 in 200 to 1 in 500. "Amniocentesis is done under ultrasound guidance, so we are usually able to avoid the placenta and the baby," observes Dr. Carolyn Thompson, an obstetrician and gynecologist from Nashville, Tennessee. Miscarriage, she notes, is usually due to the rupture of the membranes or disturbance of the blood vessels, which can lead to bleeding. The Mayo Clinic reports that the risk of miscarriage is slightly higher when amniocentesis is performed before the 15th week of pregnancy.

Equal Risk

The risk of miscarriage during amniocentesis is typically the same for all women, regardless of maternal age or other health issues, Thompson says. An anterior placenta, which occurs when your placenta attaches to the front part of your uterus, closer to your abdomen, can make the procedure more technically challenging, she notes, but does not cause a significantly higher rate of miscarriage.

Additional Risk Factors

In addition to miscarriage, amniocentesis can lead to other potential problems, the Mayo Clinic notes. For instance, if your baby moves an arm or leg during the procedure, he can be struck by the needle. Amniocentesis also can cause your amniotic fluid to leak through the vaginal opening, contributing to orthopedic problems for your baby. Rare infections also can occur, including uterine infections and infections such as hepatitis C or human immunodeficiency virus, which can be transferred from mother to child during the procedure.

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"Whether or not the benefit outweighs the risk is really up to the individual woman to decide," Thompson says. "As with assumption of any risk, only the person undertaking the risk can determine if it is worth it for her." Any adverse reactions, such as heavy bleeding, cramping, pain or fever, should be immediately reported to your doctor.

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