Effect of Targeted Aspirin Administration Based on First Trimester Combined Screening for Preeclampsia on Preterm Birth: An Interrupted Time Series Analysis

Objectives To assess the effect of an aspirin intervention program on preterm birth (PTB) rates in women identified as high‐risk for preterm preeclampsia in the first‐trimester screening. Design This is a retrospective study evaluating the impact of the intervention program on preterm birth using interrupted time series analysis (ITSA) with an ARIMA model that accounts for seasonality and autocorrelation. Setting St George's University Hospital, data collected on pregnancies between 2016 and 2022. Population Pregnant women followed from the first trimester of pregnancy. Methods An ITSA was conducted on the studied population to assess whether the introduction of an aspirin intervention program, based on first‐trimester screening, influenced preterm birth rates. Main Outcome Measures Primary outcomes included overall PTB rates, while secondary outcomes included iatrogenic preterm birth (iPTB) and spontaneous preterm birth (sPTB). Results Among 31 534 births, there were 1435 PTBs: 734 spontaneous and 701 iatrogenic. ITSA analysis revealed no significant impact of the screening program on PTB rates. There was a nonsignificant decrease in total PTB and iPTB over time, with similar trends observed for early PTB (< 34 weeks). Conclusions First‐trimester screening for preterm preeclampsia identifies women at higher risk for both preterm preeclampsia and PTB. While aspirin prophylaxis and serial assessments improve some perinatal outcomes, they do not significantly reduce spontaneous or iatrogenic PTB rates. Additional interventions will be needed to achieve a substantial reduction in PTB rates in a high‐risk population.