This sheet is about exposure to low dose aspirin in pregnancy and while breastfeeding. This information is based on available published literature. It should not take the place of medical care and advice from your healthcare provider.

What is aspirin?

Aspirin is also known as acetylsalicylic acid and has been used to reduce inflammation, fever, and pain. Aspirin can prevent blood clots and has been used to treat or help prevent conditions like heart attack and stroke. Aspirin is part of a group of drugs called non-steroidal anti-inflammatory drugs (NSAIDs).

NSAIDs, including regular and high strength aspirin, are NOT preferred pain relievers during pregnancy. In October 2020, the U.S. Food and Drug Administration (FDA) made a recommendation to avoid the use of NSAIDs, including regular strength aspirin, after 20 weeks of pregnancy, unless your healthcare provider feels it is necessary. More information about regular strength aspirin can be found in our fact sheet: https://mothertobaby.org/fact-sheets/regular-strength-aspirin/.

What is low dose aspirin?

Low dose aspirin ranges from 60 to 150 mg daily, but the usual dose taken during pregnancy to treat or prevent certain conditions is 81 mg daily.

Sometimes when people find out they are pregnant, they think about changing how they take their medication, or stopping their medication altogether. However, it is important to talk with your healthcare providers before making any changes to how you take your medication. Your healthcare providers can talk with you about the benefits of treating your condition and the risks of untreated illness during pregnancy.

I take low dose aspirin. Can it make it harder for me to get pregnant?

Low dose aspirin is not expected to make it harder to get pregnant. A study that included people who had one or two previous pregnancy losses found that taking low dose aspirin at least 4 days a week increased the chance of pregnancy.

Does taking low dose aspirin increase the chance of miscarriage?

Miscarriage is common and can occur in any pregnancy for many different reasons. Taking low doses of aspirin as directed by a healthcare provider is not expected to increase the chance of miscarriage. Some studies have shown that taking low dose aspirin before pregnancy might help lower the chance of miscarriage in some people who have had one or more miscarriages before 20 weeks of pregnancy.

Does taking low dose aspirin increase the chance of birth defects?

Every pregnancy starts out with a 3-5% chance of having a birth defect. This is called the background risk. Studies on the use of low dose aspirin during pregnancy have not found a higher chance of birth defects.

Does taking low dose aspirin in pregnancy increase the chance of other pregnancy-related problems?

Taking low dose aspirin as directed by a healthcare provider is not expected to increase the chance of pregnancy-related problems, such as preterm delivery (birth before week 37) or low birth weight (weighing less than 5 pounds, 8 ounces [2500 grams] at birth).

Studies have shown that low dose aspirin might improve pregnancy outcomes in some people by increasing blood flow to and reducing inflammation or swelling in the uterus. It may also lower the chances for preterm delivery and preeclampsia (high blood pressure and problems with organs, such as the kidneys), which can lead to seizures (called eclampsia) in people who have a higher risk of these complications. However, people who are pregnant should only take low dose aspirin under the direction and care of their healthcare provider.

Does taking low dose aspirin in pregnancy affect future behavior or learning for the child?

Limited information on low dose aspirin exposure during pregnancy does not suggest an increased chance for problems with physical or mental development in infants at 18 months of age. A study that looked at children up to 5 years of age who were born before 33 weeks of pregnancy and who were exposed to low dose aspirin during pregnancy did not find an effect on learning or behavior compared to children who were not exposed to low dose aspirin during pregnancy. Another study found no differences in neurodevelopmental outcomes in children between 33 and 39 months old after prenatal exposure to low dose aspirin.

Breastfeeding while taking low dose aspirin:

Low dose aspirin gets into breast milk in small amounts. Occasional use of low dose aspirin is not expected to increase risks to a breastfeeding infant. Regular strength aspirin (over 325 mg) is not preferred during breastfeeding. More information about regular strength aspirin can be found in our fact sheet: https://mothertobaby.org/fact-sheets/regular-strength-aspirin/. Be sure to talk to your healthcare provider about all your breastfeeding questions.

If a male takes low dose aspirin, could it affect fertility or increase the chance of birth defects?

It is not known if low dose aspirin could affect male fertility (ability to get partner pregnant) or increase the chance of birth defects above the background risk. In general, exposures that fathers or sperm donors have are unlikely to increase risks to a pregnancy. For more information, please see the MotherToBaby fact sheet Paternal Exposures at https://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy/.

Selected References:

• Abdi N, et al. 2020. The effect of aspirin on preeclampsia, intrauterine growth restriction and preterm delivery among healthy pregnancies with a history of preeclampsia. J Chin Med Assoc 83(9):852-857. [PMC free article: PMC7478204] [PubMed: 32773581]
• Annals. 2014. Summaries for patients: aspirin to prevent preeclampsia-related complications and death: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 161(11): I28. [PubMed: 25200275]
• Bloor M, Paech M. 2013. Nonsteroidal anti-inflammatory drugs during pregnancy and the initiation of lactation. Anesth Analg 116(5):1063-75. [PubMed: 23558845]
• Datta P, et al. 2017. Transfer of low dose aspirin into human milk. J Hum Lact 33(2):296-299. [PubMed: 28418802]
• Ellfolk M, Hultzsch S. 2015. Analgesics, antiphlogistics and anesthetics. In C Schaefer, P Peters, R Miller (Eds.), Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment. 3rd ed. 653-655. London: Elsevier.
• Grab D, et al. 2000. Effects of low-dose aspirin on uterine and fetal blood flow during pregnancy: results of a randomized, placebo-controlled, double-blind trial. Ultrasound Obstet Gynecol 15:19-27. [PubMed: 10776008]
• Hoffman MK, et al. 2024. Neurodevelopment of children whose mothers were randomized to low-dose aspirin during pregnancy. Obstet Gynecol 1:1-8. [PMC free article: PMC10953679] [PubMed: 38262066]
• Kupka E, et al. 2023. Low-dose aspirin use in pregnancy and the risk of preterm birth: a Swedish register-based cohort study. Am J Obstet Gynecol 228(3):336e1-336e9. [PubMed: 36096185]
• LeFevre ML, U.S. Preventive Services Task Force. 2014. Low-dose aspirin use for the prevention of morbidity and mortality from preeclampsia: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 161(11):819-26. [PubMed: 25200125]
• Maher JE, et al. 1993. The effect of low-dose aspirin on fetal urine output and amniotic fluid volume. Am J Obstet Gynecol 169:885-8. [PubMed: 8238144]
• Malm H, Borish C. 2015. Analgesics, non-steroidal anti-inflammatory drugs (NSAIDS), muscle relaxants, and antigout medications. In C Schaefer, P Peters, R Miller (Eds.), Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment, 3rd ed. 27-32. London: Elsevier.
• Marret, S. et. al. 2010. Prenatal Low-Dose Aspirin and Neurobehavioral Outcomes of Children Born Very Preterm. Pediatrics 125(1):e29-e34. [PubMed: 20026499]
• Martini A, et al. 2003. Analysis of semen from patients chronically treated with low or moderate doses of aspirin-like drugs. Fertil and Steril 80(1):221-222. [PubMed: 12849830]
• Mone F, McAuliffe FM. 2015. Preconception low-dose aspirin and pregnancy outcomes: results from the EAGeR randomized trial. Ir Med J. Jan;08(1):5. [PubMed: 25702343]
• Naimi A, et al. 2021. The Effect of Preconception-Initiated Low-Dose Aspirin on Human Chorionic Gonadotropin Detected Pregnancy, Pregnancy Loss, and Live Birth. Annals of Internal Medicine May;174(5):595-601. [PMC free article: PMC9109822] [PubMed: 33493011]
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• Schisterman EF, et al. 2015. Preconception low dose aspirin and time to pregnancy: findings from the effects of aspirin in gestation and reproduction randomized trial. J Clin Endocrinol Metab May; 100(5):1785-91. [PMC free article: PMC4422888] [PubMed: 25710565]
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