Aspirin is not recommended during pregnancy, particularly in the third trimester. If you have taken aspirin early in pregnancy or before you found out you were pregnant, don't worry. Studies have not shown aspirin in low amounts to be hazardous to baby. There are several reasons to avoid aspirin in pregnancy. Aspirin has a blood thinning effect and therefore can cause bleeding problems for mom and baby. It has been associated with placental abruption. Placental abruption is where the placenta detaches from the uterus prior to birth. This can be a very serious condition for both mom and baby. It has also been associated with jaundice after birth and bleeding problems for baby. It may also cause problems with the valves of your baby's heart closing properly
Another reason to avoid aspirin in pregnancy is it's effect on labor and childbirth. Aspirin can decrease uterine contractions which can lead to prolonged or delayed labor. Aspirin use can also increase your chances of going overdue. For the most part, aspirin should be avoided during pregnancy, however there may be some occasions where aspirin may be beneficial during pregnancy.
Some studies have shown low does of aspirin beneficial in preventing preeclampsia. Low dose baby aspirin is sometimes used in early pregnancy to prevent miscarriage where clotting or bleeding factors are suspected.
Do not take aspirin (or any other medication) without first talking to your doctor.