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11: Beyond preeclampsia: low dose aspirin reduces spontaneous preterm birth

      Objective

      Low dose aspirin (LDA) has been shown to decrease the rate of overall preterm birth (PTB), likely due to a decrease in medically indicated PTB. However, there are limited data on the effect of LDA on spontaneous preterm birth (sPTB). Our objective was to determine whether LDA reduces the rate of sPTB in low-risk nulliparous women.

      Study Design

      This is a secondary analysis of a randomized, placebo-controlled trial of LDA for prevention of preeclampsia in healthy, low-risk, nulliparous women. Low-risk women were defined by the absence of hypertension, renal disease, diabetes, other endocrine disorders, seizures, heart disease, or collagen vascular disease. Our study was limited to singleton, non-anomalous gestations. Women were eligible if they had prior pregnancy terminations, but not prior spontaneous pregnancy loss <20wks. Current pregnancies that resulted in a loss or termination <20wks, antepartum stillbirth or had missing follow-up data were excluded. The treatment intervention was 60mg of aspirin, initiated at 13-25wks gestation or matching placebo. The primary outcome was sPTB <34wks gestation. Secondary outcomes included sPTB <37 and overall PTB <37 and <34wks. Baseline demographics and primary and secondary outcomes were compared between treatment groups. A logistic regression model was used to adjust for confounders related to sPTB.

      Results

      Of 2543 included women, 1262 (49.6%) received LDA and 1281 (50.4%) placebo. Baseline characteristics were similar between groups, except for prior pregnancy terminations and marital status. The rate of sPTB <34wks was 1.03% (n=13) and 2.34% (n=30) in the LDA and placebo group, respectively (OR 0.43, 95% CI 0.26-0.84). After adjustment for variables that were clinically relevant or statistically significant, including BMI, race, prior pregnancy termination, tobacco use, marital status and education level, there was a significant reduction in sPTB <34wks in the LDA group (aOR 0.46, 95% CI 0.23-0.89). The rates of overall PTB <34 and <37wks and sPTB <37wks were similar in women that received LDA compared to placebo (table 1, figure 1).

      Conclusion

      LDA is associated with a substantial decrease in sPTB <34wks in low-risk nulliparous women. These findings suggest a new therapeutic option for PTB prevention that requires further study.
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