Is it safe to take aspirin during pregnancy?

Aspirin is a nonsteroidal anti-inflammatory drug. According to the U.S. Food and Drug Administration , pregnant women should avoid taking nonsteroidal anti-inflammatory drugs after week 19, likely due to the concern of rare fetal kidney problems and reduced amniotic fluid [1]. The typical over-the-counter and low-dose aspirin is 81 mg, also known as baby aspirin [1].

Why would the doctor recommend low-dose aspirin?

Low-dose aspirin is recommended for those at high risk of preeclampsia and should begin during the second trimester and continue until delivery [2–3].

Back in the 90s, in a multicenter clinical trial of 9,364 women, 60 mg of aspirin significantly reduced the likelihood of preterm delivery compared to placebo controls and there was a significant trend toward greater reductions in proteinuric preeclampsia [4].

Who is at risk for preeclampsia?

If you have a history of preeclampsia or pre-existing high blood pressure, diabetes, chronic kidney disease, or autoimmune disease, or you are having twins/triplets, you may be at risk [5]. Also, if this is your first baby or if you have conceived with assisted reproductive technologies, your doctor may recommend low-dose aspirin [6]. This was based on several research studies.

One study in 2004 found that aspirin significantly increased birth rate compared with no treatment in in-vitro fertilization [7].

However, a meta-analysis in 2007 comparing aspirin to placebo or no treatment groups found no significant difference in clinical outcomes, including clinical pregnancy rate per embryo transfer, spontaneous abortion or ectopic pregnancy, or live birth rate per embryo transfer [8]. Consistently, no significant difference was found in the clinical pregnancy rate and live birth rate between aspirin and placebo groups in in-vitro fertilization treatments [9–12].

Surprisingly, a 2019 study focusing on frozen-thawed embryo transfers found a higher rate of clinical pregnancy, implantation, and live birth, and a lower rate of miscarriage when patients received 100 mg aspirin compared to those receiving placebo [13].

What happened when low-dose aspirin is initiated before the second trimester? It actually reduced the risk of preterm delivery but had no negative impact on fetal growth [14].