Why should a woman be cautioned against taking acetylsalicylic acid to relieve pain in labor?

Aspirin, also known as acetylsalicylic acid, is a medication used to treat pain, fever, or inflammation. Taking aspirin regularly during pregnancy can affect your baby's heart or blood flow, so it's best to avoid aspirin unless your doctor recommends you take it. Your best bet for dealing with labor pain at home is to keep active until it's time to head to the hospital.