Generally, aspirin and ibuprofen (Advil, Motrin IB, others) aren't recommended as pain relievers during pregnancy.
Aspirin interferes with your blood's clotting action. As a result, taking aspirin during pregnancy — especially after 32 weeks — can contribute to maternal and fetal bleeding. Aspirin and ibuprofen can also cause the premature closure of a vessel in a baby's heart, which can lead to high blood pressure in the baby's lungs (pulmonary hypertension), and prolong labor.
However, low-dose aspirin therapy is sometimes prescribed during pregnancy to help treat medical conditions. If you need to take aspirin during your third trimester of pregnancy, your health care provider will likely closely monitor you and your baby.
If you need to take a pain reliever during pregnancy, ask your health care provider about the options. He or she might approve occasional use of acetaminophen (Tylenol, others).