Patient-Oriented Evidence That Matters

Low-Dose Aspirin Beneficial for the Prevention of Preterm Birth in Nulliparous Patients with Singleton Pregnancy


Am Fam Physician. 2020 Nov 15;102(9):online.

Clinical Question

Does initiating low-dose aspirin use in early pregnancy reduce the incidence of preterm birth among nulliparous patients with singleton gestation?

Bottom Line

The routine use of low-dose aspirin, 81 mg daily, starting as early as six weeks' gestational age provided a statistically significant absolute risk reduction (nearly 2 percentage points) in the incidence of preterm birth among nulliparous patients with singleton gestation in resource-poor countries. No significant treatment harms were observed, but the study was not powered to assess rare events. It is not clear whether the results can be generalized to patients in advanced economies. (Level of Evidence = 1b)


The study was carried out at seven community sites in six resource-poor countries (India, Pakistan, Zambia, Democratic Republic of Congo, Guatemala, and Kenya). The authors enrolled 11,976 nulliparous patients at least 14 years of age with singleton pregnancies and randomized them to receive 81 mg of aspirin or placebo starting between 6 0/7 and 13 6/7 weeks' gestational age and continued until 37 0/7 weeks' or delivery. Patients were excluded for allergy to aspirin, previous aspirin use for at least seven days during the pregnancy, more than two first-trimester pregnancy losses, or medical conditions that might be considered a contraindication to study participation (e.g., diabetes mellitus or hypertension). Further screening required a blood pressure of less than 140/90 mm Hg, a hemoglobin level of at least 7 g per dL (70 g per L), and a viable fetus without anomaly. For the primary outcome of preterm birth, the authors planned a modified intention-to-treat analysis to include only patients who delivered at 20 0/7 weeks' gestation or later (n = 11,558). At least 90% adherence to treatment based on pill counts was high: approximately 85%. Preterm birth before 37 0/7 weeks' occurred in 11.6% (668 out of 5,780) of patients in the aspirin group vs. 13.1% (754 out of 5,754) in the placebo

POEMs (patient-oriented evidence that matters) are provided by Essential Evidence Plus, a point-of-care clinical decision support system published by Wiley-Blackwell. For more information, see http://www.essentialevidenceplus.com. Copyright Wiley-Blackwell. Used with permission.

For definitions of levels of evidence used in POEMs, see http://www.essentialevidenceplus.com/product/ebm_loe.cfm?show=oxford.

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This series is coordinated by Sumi Sexton, MD, editor-in-chief.

A collection of POEMs published in AFP is available at https://www.aafp.org/afp/poems.



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