Pregnancy - What is Amniocentesis?

Inside the uterus, surrounding your growing baby, is a liquid called 'amniotic fluid'. A long needle is inserted through the abdomen to extract a small sample of that fluid. Using it, doctors can perform tests that indicate potential problems and provide information about the health of the gestating fetus.

Test results typically arrive in a week or two and the test is sometimes referred to as an AFT (Amniotic Fluid Test).

Typically done around 15-20 weeks, an 'amnio' can examine possible genetic abnormalities, check for uterine infections, Rh (rhesus) sensitization and other possible problems. But it can be used as a general health check as well

Only a small amount of fluid is withdrawn and is generally preceded by an ultrasound test. The fluid contains sloughed off skin and other cells from the developing fetus and these form the basis for part of the test.

Down Syndrome

Down syndrome is a rare condition, but amniotic fluid contains markers that can assist physicians in determining the odds that your child is affected. The test is about 99% accurate for Down's and is usually combined with an ultrasound and other tests.

Other genetic disorders - such as sickle cell anemia, Huntington's, Tay-Sachs or cystic fibrosis can all be diagnosed while the child is still in the womb. Only a small percentage of babies are afflicted with any of these conditions, but most women will want to perform this basic check.

Spina bifida

Spina bifida is a neural condition that can lead to crippling and amniocentesis can test for this as well, along with other neural tube defects. Even among high risk women, the odds are less than 5% that a problem will be discovered. Still, some women choose to terminate a pregnancy if the condition is discovered.

As a side benefit of the genetic screening it's possible to determine the baby's sex, though ultrasound is the more common method now.

Single Test Not Definitive

No single test is definitive, so women may want to consider multiple tests. Women 35 years or older are at higher risk of producing infants with some of the disorders discussed above. Combining amniocentesis with ultrasound or multiple marker tests can bring peace of mind.

Along with that peace of mind getting tested has other benefits. Certain in utero deficiencies can be treated to resolve problems before they become a major issue.

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The test does have some minor risks of its own, however, and this should be borne in mind. Miscarriages can be induced by amniocentesis, for example. Great care is taken to ensure that the needle doesn't puncture the baby. But, there is a small chance (about 1 in 1000) that the test will produce an uterine infection.

Few women experience any pain from the procedure, with about 1% having spotting or fluid leaking after the test. Avoiding stresses such as lifting or prolonged standing after the procedure can reduce the odds of any problems.