The role of confounding in the association between pregnancy complications and subsequent preterm birth: a cohort study

OBJECTIVE To estimate the degree of confounding necessary to explain the associations between complications in a first pregnancy and the subsequent risk of preterm birth. DESIGN Population-based cohort study. SETTING Western Australia. POPULATION Women (n = 125 473) who gave birth to their first and second singleton children between 1998 and 2015. MAIN OUTCOME MEASURES Relative risk (RR) of a subsequent preterm birth (