You will be randomly chosen (like flipping a coin) to take either 81 mg or 162 mg of aspirin each day until 36 weeks of pregnancy. These doses are often given to pregnant women in the U.S., but 162 mg hasn't been studied much. We'll collect information about you and your baby from your medical records during your hospital stay. We might also take a blood sample when you join the study and around 22 weeks of your pregnancy. We'll collect any unused medication at the end of the study or when you have your baby.