Objectives To examine the association between maternal anaemia and adverse maternal and infant outcomes, and to assess the feasibility of conducting epidemiological studies through the Indian Obstetric Surveillance System–Assam (IndOSS-Assam).

Design Retrospective cohort study using anonymised hospital records. Exposure: maternal iron deficiency anaemia; outcomes: postpartum haemorrhage (PPH), low birthweight, small-for-gestational age babies, perinatal death.

Setting 5 government medical colleges in Assam.

Study population 1007 pregnant women who delivered in the 5 medical colleges from January to June 2015.

Main outcome measures ORs with 95% CIs to estimate the association between maternal iron deficiency anaemia and the adverse maternal and infant outcomes. Potential interactive roles of infections and induction of labour on the adverse outcomes were explored.

Results 35% (n=351) pregnant women had moderate–severe anaemia. Women with severe anaemia had a higher odds of PPH (adjusted OR (aOR) =9.45; 95% CI 2.62 to 34.05), giving birth to low birthweight (aOR=6.19; 95% CI 1.44 to 26.71) and small-for-gestational age babies (aOR=8.72; 95% CI 1.66 to 45.67), and perinatal death (aOR=16.42; 95% CI 4.38 to 61.55). Odds of PPH increased 17-fold among women with moderate–severe anaemia who underwent induction of labour, and 19-fold among women who had infection and moderate–severe anaemia.

Conclusions Maternal iron deficiency anaemia is a major public health problem in Assam. Maternal anaemia was associated with increased risks of PPH, low birthweight, small-for-gestational age babies and perinatal death. While the best approach is prevention, a large number of women present with severe anaemia late in pregnancy and there is no clear guidance on how these women should be managed during labour and delivery.