Low birthweight (LBW) attributable to malaria in pregnancy is a significant risk for millions in Africa. Infants born to primigravidae are at greatest risk and it is proposed that this excess risk can be used as a simple indicator of malaria transmission and exposure in pregnant women in Africa. Birthweight data from different regions in 11 malarious and three non-malarious African countries were investigated. A regression analysis of the excess risk of low birthweight in first pregnancies, compared with later ones, was completed and interpreted in relation to malaria-transmission intensities. The aim was to develop a simple birthweight chart (nomogram) as a tool for monitoring malaria transmission or malaria control in pregnancy. Low-birthweight risk in first pregnancies was associated with levels of malaria-transmission intensity amongst different African countries. The nomogram distinguished longitudinal changes in malaria exposure, related to season and changes in antimalarial-drug policy. Malaria is one of the most important causes of LBW in first pregnancies in Africa. As birthweight and parity are routinely recorded in many delivery centres across Africa, the nomogram provides a simple, available and inexpensive tool for monitoring malaria transmission and exposure in pregnant women and the effectiveness of malaria-control activities for this high-risk group.