Women who are pregnant should be aware that taking nonsteroidal anti-inflammatory drugs (NSAIDs) 20 weeks or more into their pregnancies could serious cause kidney problems in their unborn baby. The U.S. Food and Drug Administration (FDA) has issued a warning and is requiring labeling on all NSAIDS to reflect this effect.

The kidney problems for infants, though rare, are serious and can lead to low levels of amniotic fluid. This brings the potential for pregnancy-related complications. Amniotic fluid is the liquid cushioning the baby while in the mother’s uterus and helps move water and nutrients between mother and unborn child.

The FDA warning does not apply to the use of low-dose aspirin. Though it is a NSAID, low-dose aspirin can be a helpful treatment for some women during pregnancy.

Women have already been warned not to take NSAIDs after about 30 weeks of pregnancy. Taking these painkillers during this time in their pregnancies can lead to heart issues for the unborn baby.

NSAIDs include ibuprofen, naproxen, diclofenac and celecoxib. They are available over-the-counter (OTC) and by prescription. They work by blocking the production of certain chemicals in the body that cause inflammation.

“It is important that women understand the benefits and risks of the medications they may take over the course of their pregnancy,” said Patrizia Cavazzoni, M.D., acting director of the FDA’s Center for Drug Evaluation and Research, in a statement. People have taken non-steroidal anti-inflammatories for decades to treat pain and fever from many medical conditions.

The FDA warning does not apply to the use of low-dose aspirin (81 mg). Though aspirin is also an NSAID, low-dose aspirin can be an important treatment for some women during pregnancy.

The warning is the result of cases reported to the agency about low amniotic fluid levels or kidney problems in unborn babies associated with NSAID use during pregnancy and a review of the medical literature.

After about 20 weeks of pregnancy an unborn baby’s kidneys begin producing most of the amniotic fluid on their own. Amniotic fluid, the liquid cushioning the baby while in the mother’s uterus, also helps move water and nutrients between mother and unborn child. Fetal kidney problems can cause low levels of this fluid.

Low levels of amniotic fluid may be seen after taking NSAIDs for days or weeks, but it can be detected after as little as two days of regular NSAID use. These kidney problems and reductions in amniotic fluid usually go away if the pregnant woman stops taking the NSAID.

The FDA is requiring changes to the prescribing information accompanying prescription NSAIDs. They will also have to describe the potential risk of kidney problems and subsequent low amniotic fluid in unborn babies and recommend that NSAID use be limited between about 20 weeks to 30 weeks of pregnancy.

If you are between about 20 and 30 weeks of pregnancy and your doctor believes you should still use an NSAID, limit your use to the lowest effective dose and shortest possible duration.