Placental growth factor at 24-28 weeks for aspirin discontinuation in pregnancies at high risk for preterm preeclampsia: Post hoc analysis of StopPRE trial

Introduction: This study aims to evaluate the safety of discontinuing aspirin treatment at 24-28 weeks in women at high risk after first-trimester combined screening for preeclampsia (PE) and normal placental growth factor (PlGF) levels at 24-28 weeks of gestation.

Material and methods: This is a post hoc analysis of the StopPRE trial, conducted at nine Spanish maternity hospitals from September 2019 to September 2021. In the StopPRE trial, all high-risk single pregnancies identified during first-trimester screening for PE were treated with 150 mg of daily aspirin. Out of 1604 eligible women with a soluble fms-like tyrosine kinase-1 to PlGF ratio (sFlt-1/PlGF) ≤38 at 24-28 weeks, 968 were randomly assigned in a 1:1 ratio to either continue aspirin until 36 weeks (control group) or discontinue it (intervention group). In this secondary analysis, only women with PlGF ≥100 pg/mL at 24-28 weeks were included. As in the StopPRE trial, the non-inferiority margin was set at a 1.9% difference in preterm PE incidence between the groups.

Results: Among the 13 983 screened pregnant women, 1984 (14.2%) were deemed high-risk for preterm PE, of which 397 (20.0%) were ineligible, 636 declined participation, and 32 were excluded. Ultimately, 919 women with PlGF >100 pg/mL were randomized and included in this analysis. Preterm PE occurred in 0.9% of the intervention group (4 out of 465) and 1.5% of the control group (7 out of 454), indicating non-inferiority of aspirin discontinuation. There were no significant differences between the groups in adverse pregnancy outcomes before 37 weeks, at <34 weeks, or ≥37 weeks. Minor antepartum hemorrhage incidence was significantly lower in the intervention group (absolute difference, -5.96; 95% CI, -10.10 to -1.82).

Conclusions: Discontinuation of aspirin treatment at 24-28 weeks in women with PlGF levels ≥100 pg/mL was non-inferior to continuing until 36 weeks for preventing preterm PE. However, these findings should be interpreted with caution, as they originate from a subanalysis of the StopPRE trial.