The Food and Drug Administration warned pregnant women on Thursday of using some pain and fever medications during the second half of pregnancies.

According to the FDA, these nonsteroidal anti-inflammatory drugs can cause rare but serious kidney problems in the unborn baby, which can cause pregnancy-related complications. Nonsteroidal anti-inflammatory drugs include ibuprofen, naproxen, diclofenac, and celecoxib. The FDA added that its warning does not apply to low-dose aspirin.

“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 FDA’s Center for Drug Evaluation and Research. “To this end, the agency is using its regulatory authority to inform women and their health care providers about the risks if NSAIDs are used after around 20 weeks of pregnancy and beyond.”

The FDA says that warnings on prescription nonsteroidal anti-inflammatory drugs already advise of complications past 30 weeks. The newest guidance calls on health care providers to only prescribe the lowest effective dose for the shortest period possible for women 20 to 30 weeks into their pregnancy.

More information on the warning can be found here.