Study design and setting
This study was carried out as a part of a large population-based prospective cohort study: the Rajarata Pregnancy Cohort (RaPCo). The full study design of RaPCo is published elsewhere 26. The study was carried out in the Anuradhapura district, which is the largest district in Sri Lanka. The resident population in the district is 929,539, and in 2019, 15,811 pregnant women were registered with the national maternal care programme. Of them, 12,984 were registered in field clinics before 8 weeks of gestation, 2063 were registered in field clinic visits at 8-12 weeks of gestation, and 98.6% had at least one clinic visit before delivery 27.