Prenatal maternal micronutrient supplementation has been suggested as a means to reduce the proportion of low birth weight babies in low-income countries. The effects of prenatal multi-micronutrient supplements on birth weight and perinatal mortality were studied in a randomised controlled trial among 2100 pregnant women in Guinea-Bissau. Women up to 37 weeks pregnant were individually randomised to daily supplements until delivery of A) Iron + folic acid or multi-micronutrients in B) One or C) Two recommended dietary allowances. Secondary outcomes were infant growth and maternal haemoglobin eight weeks after delivery.