The CAMMS trial is an individually randomized, unblinded, phase III trial comparing aspirin, calcium and multiple micronutrients (intervention) versus iron-folic acid (control) among 10,000 pregnant women. The primary outcome is total preterm birth, stratified by spontaneous and indicated. Eligible pregnant women will be enrolled from antenatal clinics in three study populations in Burkina Faso, Pakistan, and Zimbabwe following written informed consent.

All women attending antenatal care (ANC) who are positive on a urine pregnancy test and have a fetal ultrasound examination confirming fetal heartbeat, intrauterine pregnancy, and gestational age 6\<20 weeks' will be eligible for enrollment. Women who are \<6 weeks will be rescheduled for 2-3 weeks later. Baseline data and clinical assessments will be conducted, and women will be randomized to daily ingestion of CAMMS or IFA until delivery. In Burkina Faso, for women randomized to CAMMS, the aspirin will be withheld until 13 weeks' gestation when it can be initiated concurrently with sulfadoxine-pyrimethamine. Women will receive context-specific adherence promotion interventions designed during formative research incorporating Human-Centered Design (HCD) processes in each country. Mothers will be followed up at 4-weekly intervals throughout pregnancy plus an additional study contact (by visit, phone call, WhatsApp, or text message) at 1-2 weeks after starting the study drug to check for tolerance and adherence. Women may also be seen at closer intervals in the third trimester by the Ministry of Health clinics. Women will be encouraged to deliver in a health institution.

Between baseline and delivery, research procedures will be undertaken by research staff based at antenatal clinics during mothers' routine antenatal visits to reduce time burden on participants. Depending on gestational age at recruitment, women will receive 7-11 research visits. One additional visit or contact by text-message (SMS) or phone call will occur one-two weeks after randomization to check that the women is tolerating and correctly taking the interventions.

At delivery, infant weight and gestational age will be measured/determined by research staff based at delivery clinics or, for home deliveries, during home visits conducted within 72 hours of delivery. For infants born outside the study area or who are not reached by research staff within 72 hours, date of birth and birth weight will be transcribed from the infant's health record with source of information noted. In unusual situations where the mother and infant cannot be reached in person before 180 days postpartum but can be reached by telephone, WhatsApp, or Text message, maternal report of data of birth and birth weight will be recorded with the source of information noted. For all infants reached by a research staff member within 72 hours of birth, birth length and head circumference will be measured by standardized research staff with high quality equipment (length measured to nearest 0.1cm with infant length board and Shorr insert-tape (Weigh \& Measure LLC., Olney, MD, USA). Mothers and infants will be followed to 42 days post-partum for vital status and post-partum maternal Adverse Events (AEs) and Serious Adverse Events (SAEs). This visit may be conducted in person, by telephone, WhatsApp or text message with the source of information recorded.