Objective To estimate the burden and assess prenatal and postnatal determinants of illnesses experienced by children residing in a semiurban slum, during the first 1000 days of life.

Design Community-based birth cohort

Setting Southern India

Participants Four hundred and ninety-seven children of 561 pregnant women recruited and followed for 2 years with surveillance and anthropometry.

Main outcome measure Incidence rates of illness; rates of clinic visits and hospitalisations; factors associated with low birth weight, various illnesses and growth.

Results Data on 10 377.7 child-months of follow-up estimated an average rate of 14.8 illnesses/child-year. Gastrointestinal and respiratory illnesses were 20.6% and 47.8% of the total disease burden, respectively. The hospitalisation rate reduced from 46/100 child-years during infancy to 19/100 child-years in the second year. Anaemia during pregnancy (OR=2.3, 95% CI=1.08 to 5.18), less than four antenatal visits (OR=6.8, 95% CI=2.1 to 22.5) and preterm birth (OR=3.3, 95% CI=1.1 to 9.7) were independent prenatal risk factors for low birth weight. Female gender (HR=0.88, 95% CI=0.79 to 0.99) and 6 months of exclusive breast feeding (HR=0.76, 95% CI=0.66 to 0.88) offered protection against all morbidity. Average monthly height and weight gain were lower in female child and children exclusively breast fed for 6 months.

Conclusions The high morbidity in Indian slum children in the first 1000 days of life was mainly due to prenatal factors and gastrointestinal and respiratory illness. Policymakers need disease prevalence and pathways to target high-risk groups with appropriate interventions in the community.