Changes in rate of preterm birth and adverse pregnancy outcomes attributed to preeclampsia after introduction of a refined definition of preeclampsia: a population-based study.

INTRODUCTION Since 2013, various guidelines for hypertension in pregnancy have been refined, no longer requiring proteinuria as a requisite criterion for preeclampsia. We aimed to evaluate the impact of the new definition on preterm birth (PTB) and adverse pregnancy outcomes. MATERIAL AND METHODS Women delivering in Ontario between April 2012 and November 2016 were included. Delivery <24+0/7 weeks, major fetal anomalies or preexisting renal disease were excluded. The primary outcome was livebirth <37, <34 or <32 weeks. Rates, adjusted rate ratios (aRR) and ratio of the rate ratio (RRR) were used to compare outcomes in the 2 years after the new Society of Obstetricians and Gynaecologists of Canada (SOGC) guideline (December 2014-November 2016; period 2) vs the 2 years before (April 2012-March 2014; period 1), among women with and without preeclampsia. RESULTS In all, 268 543 and 267 964 births in periods 1 & 2, respectively, were included. Respective preeclampsia rates increased significantly from 3.9% to 4.4% (p < 0.001), with no change in maternal morbidity rates. In preeclamptic women, respective rates of PTB <37 weeks were 21.0% and 20.7% (aRR 1.01, 95% confidence interval [CI] 1.00-1.02), with significant aRR for PTB <34 (0.86, 95% CI 0.77-0.96) and <32 weeks (0.79, 95% CI 0.67-0.94). A similar aRR was observed in women without preeclampsia. In preeclamptic women, composite severe neonatal morbidity decreased after guideline change (aRR 0.95, 95% CI 0.91-0.99), a finding not observed in women without preeclampsia (RRR 0.95, 95% CI 0.91-0.99). CONCLUSIONS The new definition of preeclampsia was associated with increased disease rates, a modest reduction in adverse neonatal outcomes and no change in maternal outcomes.