In every pregnancy, a woman starts out with a 3-5% chance of having a baby with a birth defect. This is called her background risk. This sheet talks about whether exposure low dose Aspirin may increase the risk for birth defects over the background risk. This information should not take the place of medical care and advice from your health care provider.

What is low dose aspirin?

Aspirin is also known as acetylsalicylic acid (pronounced uh-seet-l-sal-uh-sil-ik). It is a common prescription and over-the-counter medication that is similar to non-steroidal inflammatory (NSAIDs) like Ibuprofen (motrin) and naproxen (Aleve), aspirin reduces inflammation, fever and pain. Aspirin can prevent the formation of blood clots which can make it useful in treating or preventing some conditions like heart attacks and strokes. The dosage for aspirin can range from 50 to 6000 milligrams (mg) per day depending on the condition being treated, and aspirin may be used in combination with other medications. Low dose aspirin ranges from 60-150 mg daily but the usual dose taken during pregnancy is 81 mg daily. Regular strength aspirin is NOT a preferred pain reliever during pregnancy.

Can taking low dose aspirin during pregnancy increase the risk of miscarriage?

Taking low doses of aspirin is not thought to increase the risk of miscarriage. For women who have had multiple miscarriages, it is thought that low dose aspirin could improve pregnancy outcomes by increasing blood flow and reducing inflammation or swelling in the uterus. We don’t yet know how effective aspirin may be in reducing the risk of miscarriage because some studies have shown a benefit, while others have not.

Most studies have looked at women who started using aspirin after becoming pregnant, but the results from a few other studies suggest that using low dose aspirin before conceiving may help improve outcomes for women who have had one or more previous miscarriages before 20 weeks of pregnancy. These findings are similar to studies that showed improved pregnancy outcomes for women who were undergoing assisted reproduction technologies and were treated with low dose aspirin prior to implantation of the fertilized egg into the uterus. More research is needed.

Can taking low dose aspirin increase the risk of birth defects during pregnancy?

Studies have consistently shown that taking low dose aspirin does not increase risks for birth defects. Some studies have shown increased risk for having a baby with a birth defect when women have taken high doses of aspirin. However, low dose aspirin is considered compatible in all trimesters of pregnancy when medically needed.

I heard that low dose aspirin can be recommended during pregnancy? Why?

Results from many studies have shown that the use of low dose aspirin can lower the chances for preeclampsia in women who are at high risk for this condition. Preeclampsia may be diagnosed when a woman develops dangerously high blood pressure and protein in the urine. Preeclampsia can lead to serious health problems for both mom and baby, including preterm birth and low birth weight. It is thought that aspirin’s ability to reduce inflammation and increase blood flow could counter the processes involved with preeclampsia. Many health organizations including American Congress of Obstetrician and Gynecologists (ACOG), the World Health Organization (WHO), the American Heart Association (AHA) and the American Academy of Family Physicians (AAFP) have recommended treatment with low dose aspirin for women at high risk for preeclampsia from 12 weeks of pregnancy until time of delivery. Only take low dose aspirin during pregnancy if your doctor recommends it.

Are there long term effects from taking low dose aspirin in pregnancy?

There is limited information about long term effects for children exposed to low dose aspirin during pregnancy. However, studies have not found an increased risk for problems with physical or mental development for infants at 18 months of age. Another study that looked at children up to 5 years of age who were born very early (before 33 weeks) and who were exposed to low dose aspirin during pregnancy did not find an effect on learning or behavioral skills compared to unexposed children.

Can I take low doses of aspirin while I am breastfeeding?

Regular strength aspirin is not the pain reliever of choice during breastfeeding. Only small amounts of low dose aspirin enter the breast milk. The occasional use of low dose aspirin (81mg daily to below 300mg daily) would not be expected to increase risks to a breastfeeding infant.

This is not the case with taking higher amounts of aspirin, where there is some concern about the medication’s ability to reduce blood clotting and, in some cases where infection is present, cause liver damage to the baby. These effects are not likely with low dose aspirin but aspirin eliminates from the infant body more slowly than from an adult’s body, so levels in the infant’s body could increase over time with long term use. In some cases treatment with low dose aspirin may be required by your health care provider.

What if the father of the baby is taking low doses of aspirin?

There is very limited information available about the effects of low dose aspirin on male reproduction. There was a study on men who attended an infertility clinic and were taking non-prescribed low dose aspirin for at least six months. There was a decrease in the amount and quality of sperm especially for those who used higher amounts of aspirin. Presently, it is not considered necessary for men to discontinue the use of low dose aspirin prior to pregnancy. However, men undergoing fertility treatment may want to talk with their health care provider about stopping aspirin if their semen analysis is abnormal. In general, exposures that fathers have are unlikely to increase risks to a pregnancy. For more information, please see the MotherToBaby fact sheet Paternal Exposures and Pregnancy at

References Available Upon Request.