A randomized double-blind controlled trial will be carried out in which young, nulliparous (having never given birth) women will be randomly assigned to receive weekly supplementation with either iron and folic acid or folic acid alone. Women will be followed-up weekly up to 18 months. Women who become pregnant will be followed-up until delivery. Malaria risk in both groups will be compared by assessing the prevalence of peripheral parasitaemia at the first antenatal clinic visit for pregnant women and at the end of the first malaria transmission season for non-pregnant women. The incidence of clinical malaria will be assessed by active and passive case detection throughout the follow-up period.