Beside its proven efficacy in preventing preeclampsia,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).

       So a trial of LDA for prevention of preeclampsia in healthy, low-risk, nulliparous women was conducted . Low-risk women were defined by the absence of hypertension, renal disease, diabetes, other endocrine disorders, seizures, heart disease, or collagen vascular disease. 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.

              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.

          Thus it was established by the study that LDA is associated with a substantial decrease in sPTB <34wks in low-risk nulliparous women.