Aspirin Risks Unclear for Postpartum Bleeding

Tara Haelle

February 07, 2022

Low-dose aspirin may increase risk of postpartum bleeding if patients don't discontinue its use at least 7 days before delivery, but it's otherwise unclear whether its use increases bleeding risk, according to research presented Feb. 5 at the meeting sponsored by the Society for Maternal-Fetal Medicine.

"These findings were a little surprising to me because we have generally been taught that aspirin is safe to continue up until delivery with minimal risk," Jenny Mei, MD, a maternal-fetal medicine fellow at the University of California, Los Angeles, said in an interview after attending the presentation. "Theoretically it makes sense that it may increase bleeding risk, but multiple studies in the past analyzing its use with gynecological surgery show minimal risk, which was conferred to the obstetrical population as well."

She noted, however, that patients prescribed low-dose aspirin already have risk factors that may increase their risk of postpartum bleeding, and the study's finding of possible increased risk was not statistically significant after accounting for those confounders. "I wouldn't change my practice management over it, but it does raise awareness that all interventions likely come with some risk," Mei said.

Hypertensive disorders of pregnancy are responsible for 6.6% of U.S. pregnancy-related deaths. The SMFM currently recommends low-dose aspirin starting at 12 weeks' gestation in patients at high risk for preeclampsia, which includes people with multifetal gestation, chronic hypertension, pregestational diabetes, renal disease, autoimmune disease, or a history of preeclampsia. However, previous research has shown mixed results on the safety of low-dose aspirin in terms of bleeding risk, Kelsey White, MD, a second-year maternal-fetal medicine fellow of the Yale University, New Haven, Conn., told attendees.

This retrospective study compared a bleeding composite endpoint among those who did and did not take low-dose aspirin between January 2018 and April 2021. The composite included an estimated blood loss of greater than 1,000 mL, postpartum hemorrhage based on ICD-9/10 code diagnosis, and red blood cell transfusion. The researchers also compared bleeding risk within the aspirin group based on discontinuation at greater or less than 7 days before delivery.

Among 16,980 patients, 11.3% were prescribed low-dose aspirin. The patients prescribed low-dose aspirin significantly differed from those not prescribed it in all demographic and clinical characteristics except placenta accreta spectrum. The average age of the aspirin group was 39 years, compared with 24 years in the nonaspirin group (P < .01). More of the aspirin group patients were Hispanic and Black, and 52.3% of patients taking aspirin had a body mass index greater than 30 kg/m2, compared with 22.9% of the nonaspirin group. Rates of diabetes, lupus, fibroids, nonaspirin anticoagulation use, cesarean delivery, and preterm delivery were all greater in the aspirin group.

In addition, 43.9% of the patients in the aspirin group had a hypertensive disorder, including 20.2% with preeclampsia, compared with 17.1% with hypertensive disorders, including 6.2% with preeclampsia, in the group not taking aspirin (P < .0001). "This shows that a high-risk population was prescribed aspirin, which correlates to the recommended prescription guidelines," White said.

The postpartum bleeding composite outcome occurred in 14.7% of patients in the low-dose aspirin group, compared with 9.2% of patients in the nonaspirin group, for an unadjusted 1.7 times greater risk of bleeding (95% confidence interval, 1.49-1.96). After adjustment for confounders, the risk declined and was no longer statistically significant (aOR = 1.15; 95% CI, 0.98-1.34).

Meanwhile, 15% of those who discontinued aspirin within 7 days of delivery had postpartum bleeding, compared with 9% of those who discontinued aspirin at 7 or more days before delivery (P = .03).

Therefore, while the study found only a possible, nonsignificant association between low-dose aspirin and postpartum bleeding, risk of bleeding was significantly greater among those who discontinued aspirin only in the last week before delivery.

"Our study is timely and supports a recent Swedish study [that] found an increased risk of intrapartum bleeding, postpartum hemorrhage, and postpartum hematoma," White said. She also noted that the United States Preventive Services Task Force changed their recommendation in 2021 for low-dose aspirin prophylaxis for cardiovascular disease.

"They now recommend against the use of low-dose aspirin for prevention in adults without a history of cardiovascular disease," White said. "The change in recommendations came after recent randomized control trials showed that low-dose aspirin had very little benefit and may increase the risk of bleeding."

However, White added that they "do not believe this study should be used to make any clinical decisions." While the study had a large sample size, it was limited by its retrospective reliance on EMR data, including the EMR medication list, and the researchers couldn't assess patient compliance or patient use of over-the-counter aspirin not recorded in the EMR.

Deirdre Lyell, MD, a professor of maternal-fetal medicine at Stanford (Calif.) University, agreed that the findings should not impact clinical practice given its limitations.

"The investigators could not entirely identify who stopped low-dose aspirin and when. When they estimated timing of stoppage of low-dose aspirin, their data suggested a small benefit among those who discontinued it at least 7 days before delivery, though this should be interpreted with caution, given the potential inaccuracy in these data," Lyell, who was not involved in the study, said in an interview. "Their study did not examine factors that should be used to confirm if there are real differences in blood loss, such as changes in blood counts before and after delivery, or more use of medications that we use to stop heavy bleeding."

In fact, Lyell noted, other research at the SMFM meeting found "that low-dose aspirin is not used frequently enough in patients who might benefit, such as those at high risk for preeclampsia," she said. "Low-dose aspirin among those at increased risk has been shown to reduce rates of preeclampsia, reducing the likelihood of risky situations for moms and babies."

The authors had no disclosures. Lyell has consulted for Bloomlife, a uterine contraction and fetal monitor. White and Mei had no disclosures.

This article originally appeared on, part of the Medscape Professional Network.


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