Berger H, Melamed N, Davis BM, et al. - This study seeks to ascertain the effect of pre-pregnancy diabetes mellitus (D), obesity (O) and chronic hypertension (H) on preterm birth (PTB). Between 2012–2016, researchers performed a retrospective population-based cohort study in Ontario, Canada. They recruited women who had a singleton livebirth or stillbirth at > 20 weeks gestation in the cohort. The primary endpoint included PTB at 24^1/7to 36^6/7weeks. There were 506,483 women who were eligible for analysis. This analyses applied multivariable Poisson regression models with robust error variance to generate relative risks (RR), further adjusted for maternal age and parity. Combinations of DOH significantly magnify the risk of PTB, especially provider initiated PTB, and PTB with altered fetal growth or preeclampsia.