Low dose aspirin (81 mg/day), also known as baby aspirin, can be used preventatively for several different reasons before and during pregnancy. Aspirin is a non-steroidal anti-inflammatory drug (NSAID) that reduces inflammation and also affects the way blood clots. Some women take aspirin while trying to conceive (TTC) and during pregnancy in hopes of preventing pregnancy loss. Others are instructed to take aspirin due to high blood pressure or to prevent preeclampsia. So what does aspirin do for pregnancy, and who should be taking it?
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Is aspirin safe for TTC and pregnancy?
Low dose aspirin is generally thought to be very safe during pregnancy and TTC, and has been well-established for use during pregnancy for a variety of conditions. While TTC, low dose aspirin does not make it any harder to become pregnant. Those with a history of pregnancy loss may experience an improved chance of becoming pregnant if taking aspirin while TTC. We’ll take a closer look at the evidence for that in a bit. Taking low dose aspirin also doesn’t increase the risk of miscarriage or pregnancy loss, and per the research appears to reduce the risk.
Studies on the use of low dose aspirin have also shown that there is no increased risk of birth defects, pre-term delivery, or low birth weight. There is not much literature looking at the physical and neurological development of children who were exposed to low dose aspirin in utero, but the evidence that is out there also shows good safety and no differences in development.
What are the risks of taking low dose aspirin?
Remember, even though low dose aspirin is safe during pregnancy, you should still talk with your provider before starting a new medication during pregnancy. Your provider can make sure that it is a good fit for you and your specific circumstances and needs.
Potential side effects of low dose aspirin are nausea, vomiting, rash or hives, diarrhea, bleeding stomach ulcers, a bleeding stroke, vaginal bleeding, and allergic reaction. People who are allergic to aspirin could also experience asthma. Those who have a bleeding or clotting disorder causing reduced clotting or those with a history of bleeding stomach ulcers should likely not take aspirin.
The good news is that low dose aspirin in pregnant women is well-tolerated. In fact, in a study of low and middle income countries, there was no statistically significant difference in emergency medical visits for the women taking aspirin vs those that did not. There was also no increase in the risk of any of the potential side effects. That means that the women taking the low dose aspirin were no more likely to experience nausea, vomiting, rash or hives, diarrhea, vaginal bleeding or allergic reaction than any of the women who were not taking low dose aspirin.
Aspirin to reduce risk of pregnancy loss for those with recurrent miscarriage
Several studies have come out of the EAGeR trial which have helped us learn more about low dose aspirin for women who have had previous pregnancy loss. In the EAGeR trial, women with 1-2 pregnancy losses took low dose aspirin daily while TTC up to 6 cycles. If the women became pregnant, they continued taking the low dose aspirin through the 36th week of gestation.
Overall, this showed that low dose aspirin didn’t increase risks during pregnancy, and that low dose aspirin did improve outcomes. In this study, the use of aspirin was not associated with any increase in bleeding. Women were instructed to take the low dose aspirin every day, but some women were not as compliant with the instructions. Even so, it was found during that study that if women took aspirin 4 days or more out of every week, they experienced the benefits of aspirin.
The women who began taking the low dose aspirin while TTC had more detectable pregnancies than the group who did not take aspirin. Those who took low dose aspirin also had fewer pregnancy losses and 30% more live births. Taking aspirin during pregnancy before 20 weeks gestation was found to be helpful, but the benefits were greater for those who started aspirin earlier in pregnancy. The best outcomes were for those who started taking the low dose aspirin while TTC.
Inflammation, hsCRP, and aspirin
Further studies of the results of the EAGeR trial have shown that not all women with history of pregnancy loss get equal benefit from taking low dose aspirin. They found that women who had the most benefit from taking low dose aspirin had high serum high-sensitivity C-reactive protein (hsCRP). C-reactive protein is made in the liver, and levels are higher when there is inflammation in the body. hsCRP levels can be measured with a blood test.
Higher levels of inflammation are associated with recurrent pregnancy loss, as well as with pelvic inflammatory disease (PID), polycystic ovary syndrome (PCOS), and endometriosis. Women with low and mid-levels of hsCRP have better pregnancy outcomes than those with high levels of hsCRP. But, when women with high levels of hsCRP took low dose aspirin, they had increased live birth rates from 44% to 59%. For those with low or mid-levels of hsCRP, there was not a statistically significant improvement in outcomes.
American College of Obstetrics and Gynecology (ACOG) does not recommend low dose aspirin for prevention of pregnancy loss at this time.
What does this all mean for those with history of pregnancy loss?
Not every woman who is TTC or pregnant should be taking aspirin. Studies do show aspirin is helpful in improving outcomes in women with a history of pregnancy loss. If you have had a pregnancy loss or recurrent pregnancy loss, it is worth the conversation with your provider about low dose aspirin. Also, if you are concerned, it may be worth asking your provider about a blood test for hsCRP. I would not recommend that you take aspirin without consulting with your provider, since taking aspirin does cause a risk of bleeding.
Aspirin to reduce risk of preeclampsia
The use of low dose aspirin to reduce risk of preeclampsia is well-established. The American College of Obstetricians and Gynecologists (ACOG) recommends low-dose aspirin for prevention of preeclampsia in women at high risk of preeclampsia. Low dose aspirin should be started between 12 weeks and 28 weeks of gestation and continued until delivery. Low dose aspirin should also be considered for women with several moderate risk factors for preeclampsia. To see a list of risk factors for preeclampsia, read this from ACOG.
The studies that I read regarding the use of low dose aspirin for reduction in risk of preeclampsia showed clear benefits. In one double-blind, placebo-controlled trial, the group who took aspirin had a more than 60% reduction in the rate of preeclampsia as compared to the placebo group. And in this study, there was no difference between the aspirin group and the placebo group in adverse effects or negative outcomes, so the aspirin was shown to be a safe and effective intervention.
Aspirin for antiphospholipid syndrome
Antiphospholipid syndrome is a blood clotting disorder that can lead to increased risk of fetal loss, preeclampsia, growth restriction, placental insufficiency, and preterm delivery. In those who have antiphospolipid syndrome, it is important to work closely with a medical professional while TTC, during pregnancy, and in the postpartum period for the safety of the mother and baby. The treatment usually consists of heparin and low dose aspirin, which has been shown to improve outcomes. It can reduce pregnancy loss in those with recurrent miscarriage due to antiphospholipid syndrome. It can also reduce the risk of preeclampsia, placental insufficiency, preterm birth, and clotting.
Citations
- Naimi AI, Perkins NJ, Sjaarda LA, Mumford SL, Platt RW, Silver RM, Schisterman EF. The Effect of Preconception-Initiated Low-Dose Aspirin on Human Chorionic Gonadotropin-Detected Pregnancy, Pregnancy Loss, and Live Birth : Per Protocol Analysis of a Randomized Trial. Ann Intern Med. 2021 May;174(5):595-601. doi: 10.7326/M20-0469. Epub 2021 Jan 26. PMID: 33493011; PMCID: PMC9109822.
- https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2018/07/low-dose-aspirin-use-during-pregnancy
- Sjaarda LA, Radin RG, Silver RM, Mitchell E, Mumford SL, Wilcox B, Galai N, Perkins NJ, Wactawski-Wende J, Stanford JB, Schisterman EF. Preconception Low-Dose Aspirin Restores Diminished Pregnancy and Live Birth Rates in Women With Low-Grade Inflammation: A Secondary Analysis of a Randomized Trial. J Clin Endocrinol Metab. 2017 May 1;102(5):1495-1504. doi: 10.1210/jc.2016-2917. PMID: 28323989; PMCID: PMC5443323.
- Connell MT, Sjaarda LA, Radin RG, Kuhr D, Mumford SL, Plowden TC, Silver RM, Schisterman EF. The Effects of Aspirin in Gestation and Reproduction (EAGeR) Trial: A Story of Discovery. Semin Reprod Med. 2017 Jul;35(4):344-352. doi: 10.1055/s-0037-1606384. Epub 2017 Oct 16. PMID: 29036741; PMCID: PMC6234510.
- https://www.ncbi.nlm.nih.gov/books/NBK582805/
- https://www.nejm.org/doi/full/10.1056/NEJMoa1704559
- https://www.aafp.org/pubs/afp/issues/2006/0701/p184.html