Impact of Aspirin on Timing of Birth in Pregnancies With Clinical Manifestations of Placental Dysfunction: Evidence From a Multicentre Randomised Clinical Trial.

OBJECTIVE To examine whether aspirin delays gestational age at delivery (GAD) in pregnancies with placental dysfunction (PD) phenotypes (preeclampsia [PE], small-for-gestational-age [SGA], placental abruption and/or stillbirth). DESIGN A secondary analysis of a multicentre stepped-wedge cluster randomised trial. SETTING 18 maternity/diagnostic units in Asia. POPULATION Singleton pregnancies examined at 11-13+6 weeks. METHODS A model in which the effect of aspirin is to delay the GAD in pregnancies with PD was developed. MAIN OUTCOME MEASURES GAD in pregnancies with PD. RESULTS Aspirin administration was associated with a significant reduction in PD < 32 weeks (adjusted relative risk 0.543, 95% CI: 0.330-0.864), with a trend for an increase of PD ≥ 32 weeks (test for trend, p-value = 0.0018). Similar findings were observed individually for PE, SGA and/or placental abruption. At 24 weeks, the aspirin-induced prolongation of pregnancies with PD was 2.85 weeks (95% CI: 0.44-5.40), and this effect was decreased by -0.19 weeks (95% CI: -0.33 to -0.05) for each week of gestation; therefore, at 28 and 32 weeks' gestation, the aspirin-induced prolongation was 2.09 and 1.33 weeks, respectively. CONCLUSIONS In this secondary analysis of a cluster randomised trial, women at high risk of PE who are destined to develop a clinical spectrum of PD may benefit from longer pregnancy duration through aspirin administration in early pregnancy. Aspirin may delay the GAD due to PD, particularly benefiting those deliveries that would occur at earlier gestations without aspirin administration.