Urinary 8-hydroxy-2′-deoxyguanosine levels and preterm births: a prospective cohort study from the Japan Environment and Children’s Study

Objectives To evaluate the association between urinary 8-hydroxy-2′-deoxyguanosine (U8-OHdG) level—a marker of oxidative stress—and the incidence of preterm births (PTBs).Design Prospective cohort study.Setting The Japan Environment and Children’s Study (JECS).Participants Data from 92 715 women with singleton pregnancies at and after 22 weeks of gestation who were enrolled in the JECS, a nationwide birth cohort study, between 2011 and 2014 were analysed. U8-OHdG levels were assessed once in the second/third trimester using liquid chromatography–tandem mass spectrometry. Participants were categorised into the following three or five groups: low (