Prenatal arsenic exposure, child marriage, and pregnancy weight gain: Associations with preterm birth in Bangladesh.

•In Bangladesh, the prevalence of preterm birth is very high.•Common risk factors are arsenic exposure, child marriage & perinatal undernutrition.•Arsenic exposure & child marriage are associated with higher risk of preterm birth.•Pregnancy weight gain is associated with lower risk of preterm birth.•Adequate nutrition among women with a history of child marriage is important.