Widespread legalisation of marijuana raises safety concerns for its use in pregnancy. This study investigated the association of marijuana use prior to and during pregnancy with pregnancy outcomes in a prospective cohort of 5588 nulliparous women from the international SCOPE study. Women were assessed at 15 ± 1 and 20 ± 1 weeks’ gestation. Cases [278 Preeclampsia, 470 gestational hypertension, 633 small-for-gestational-age, 236 spontaneous preterm births (SPTB), 143 gestational diabetes] were compared separately with 4114 non-cases. Although the numbers are small, continued maternal marijuana use at 20 weeks’ gestation was associated with SPTB independent of cigarette smoking status [adj OR 2.28 (95% CI:1.45–3.59)] and socioeconomic index (SEI) [adj OR 2.17 (95% CI:1.41–3.34)]. When adjusted for maternal age, cigarette smoking, alcohol and SEI, continued maternal marijuana use at 20 weeks’ gestation had a greater effect size [adj OR 5.44 (95% CI 2.44–12.11)]. Our data indicate that increasing use of marijuana among young women of reproductive age is a major public health concern. ; Shalem Y. Leemaqz, Gustaaf A. Dekker, Lesley M. McCowan, Louise C. Kenny, Jenny E. Myers, Nigel A.B. Simpson, Lucilla Poston, Claire T. Roberts, On behalf of the SCOPE Consortium