Determinants of low birthweight, small-for-gestational-age and preterm birth in Lombok, Indonesia: analyses of the birthweight cohort of the SUMMIT trial.

Objective: To examine the determinants of low birthweight (LBW), small-for-gestation (SGA) and preterm births in Lombok, Indonesia, an area of high infant mortality.

Methods: Data from The Supplementation with Multiple Micronutrient Intervention Trial (SUMMIT), a double-blind cluster-randomised controlled trial, were analysed. The odds ratio of factors known to be associated with LBW, SGA and preterm birth was assessed and adjusted for the cluster design of the trial using hierarchical logistic regression. Determinants included constitutional, demographic and psychosocial factors, toxic exposure, maternal nutrition and obstetric history and maternal morbidity during and prior to pregnancy. Population attributable risks of modifiable determinants were calculated.

Results: A cohort of 14,040 singleton births was available for analysis of LBW, with 13,498 observations for preterm births and 13,461 for SGA births. Determinants of LBW and SGA were similar and included infant's sex, woman's education, season at birth, mothers' residence, household wealth, maternal mid-upper arm circumference (MUAC), height and a composite variable of birth order and pregnancy interval. Socioeconomic indicators were also related to preterm births and included mother's education, residence and household wealth, while nutritional-related factors including low MUAC and birth order and interval were associated with preterm birth but not maternal height. Nausea was protective of preterm birth, while diarrhoea was associated with higher odds of preterm birth. Oedema during pregnancy was protective of SGA but associated with higher odds of preterm delivery. Around 33%, 13% and 13% of the determinants of LBW, SGA and preterm births were preventable.

Conclusion: Women's education, maternal nutrition and household wealth and family planning are key factors to improving birth outcomes.