Between 50% and 70% of pregnant women experience back pain related to their pregnancy, and for 10% of them, it's so severe that they cannot continue working or enjoying daily activities. Easing the discomfort can be difficult. The Food and Drug Administration says that NSAIDs (nonsteroidal anti-inflammatory drugs) like aspirin, ibuprofen, naproxen, diclofenac, and celecoxib are to be avoided after the 20th week of pregnancy because they can cause rare but serious kidney problems in an unborn baby that lead to low levels of amniotic fluid surrounding the baby and additional complications.