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Low-dose aspirin beneficial for the prevention of preterm birth in nulliparas with singleton pregnancy
Clinical Question
Does low-dose aspirin starting in early pregnancy reduce the incidence of preterm birth among nulliparous women with singleton gestation?
Bottom line
The routine use of low-dose aspirin — 81 mg daily — starting as early as 6 weeks' gestational age provided a statistically significant absolute risk reduction (nearly 2 percentage points) in the incidence of preterm birth among nulliparous women with singleton gestation in resource-poor countries. No significant treatment harms were observed, though the study was not powered to assess rare events. It is not clear whether the results are generalizable to women in advanced economies. 1b
Reference
Study design: Randomized controlled trial (double-blinded)
Funding: Government
Setting: Outpatient (primary care)
Synopsis
This study was carried out at 7 community sites in 6 resource-poor countries (India, Pakistan, Zambia, Democratic Republic of Congo, Guatemala, and Kenya). The authors enrolled 11,976 nulliparous women at least 14 years old with singleton pregnancies and randomized them to receive 81 mg aspirin or placebo starting between 6 0/7 and 13 6/7 weeks' gestational age and continued until 37 0/7 weeks' or delivery. Women were excluded for allergy to aspirin, previous aspirin use for at least 7 days during the pregnancy, more than 2 first-trimester pregnancy losses, or medical conditions that might be considered a contraindication to study participation (eg, diabetes or hypertension). Further screening required a blood pressure of less than 140/90 mm Hg, a hemoglobin level at least 7.0 g/dL, 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 women 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% (668/5780) of women in the aspirin group versus 13.1% (754/5754) of women in the placebo group (relative risk [RR] 0.89; 95% CI 0.81 - 0.98; P = .012; number needed to treat = 66; 37 - 308). The authors estimated the absolute risk difference at 2%. More than 20 secondary outcomes were considered and treated as exploratory. Among those outcomes that were statistically significant and better in the aspirin group were early preterm delivery (< 34 weeks') and fetal loss after 16 weeks' gestation and up to 7 days postpartum. There were no differences in the overall incidence of hypertensive disorders, maternal bleeding problems, and fetal growth abnormalities. There were no statistically significant harms of aspirin treatment, although the study was not powered to assess rare catastrophic outcomes.
Reviewer
Linda Speer, MD
Professor and Chair, Department of Family Medicine
University of Toledo
Toledo, OH
Comments
Level 1 evidence
So now every obstetrician is obliged to counsel and recommend daily ASA for all nulliparous women for the 1.5% benefit -- if it makes it to the guidelines. Because practice today is driven by the whip of the College.