Impact of ACOG Guideline Regarding Low Dose Aspirin for Prevention of Superimposed Preeclampsia [27O]

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In July 2016, an American College of Obstetricians and Gynecologists (ACOG) guideline recommended that pregnant women with chronic hypertension (CHTN) be offered low dose aspirin to prevent superimposed preeclampsia (SIP). This study aimed to evaluate the incidence of SIP in women with CHTN before and after the ACOG guideline.


This retrospective cohort study included CHTN patients who delivered at Thomas Jefferson University Hospital from 1/2008 to 7/2017, excluding multiple gestations. The cohort was divided into 2 groups, before and after the ACOG recommendation. We offered daily 81 mg aspirin. The cohort was stratified by other risk factors for SIP, including history of preeclampsia and pre-gestational diabetes. The primary outcome was incidence of SIP. Secondary outcomes were incidence of SIP with severe features (SIPSF), small for gestational age, and preterm birth.


We identified 715 pregnant CHTN patients, comprised of 80 post-ACOG and 635 pre-ACOG patients. The incidence of SIP in all women with CHTN was 20 (25%) vs 232 (37%), OR 0.43 (95% CI 0.26-0.73). SIP and SIPSF were significantly decreased in the subgroup of women with CHTN without other risk factors: 4/41 (10%) vs 106/355 (30%), OR 0.25 (95% CI 0.08-0.73); and 2/41 (5%) vs 65/355 (18%), OR 0.22 (95% CI 0.54-0.97), respectively. Maternal demographics and secondary outcomes were not significantly different.


After the ACOG guideline, low dose aspirin decreased SIP by 57% in all women with CHTN. The benefit was higher in women with CHTN without other risk factors, with decreases of 75% in SIP and 78% in SIPSF.

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