Antenatal Vitamin D3 Supplementation in Bangladesh: Randomized Controlled Trial

Inclusion Criteria: * Women aged 18 to \<35 years. * Current residence in Dhaka at a fixed address * Plans to have the delivery performed at the Shimantik maternity center, and to stay in Dhaka throughout the pregnancy and for at least one month past the date of delivery. * Gestational age of 26th to 29th (inclusive), estimated based on the first day of the last menstrual period (LMP). Exclusion Criteria: * Use of any dietary supplement containing more than 400 IU/day (10 mcg/day) of vitamin D within the month prior to enrolment, or refusal to stop taking supplemental vitamin D at any dose after enrollment. * Current use of anti-convulsant or anti-mycobacterial (tuberculosis) medications. * Severe anemia (hemoglobin concentration \< 70 g/L). * Complicated medical or obstetric history that may increase the risk of preterm birth or labor/delivery complications, based on self-report or clinical assessment by physician (e.g., cardiovascular disease, uterine hemorrhage, placenta previa, threatened abortion, hypertension, preeclampsia, preterm labor, or multiple gestation). * Prior history of delivery of an infant with a major congenital anomaly, birth asphyxia, or perinatal death (stillbirth or death within first week of life).