Malaria infection of the placenta in The Gambia, West Africa; its incidence and relationship to stillbirth, birthweight and placental weight.

The incidence of placental malaria at parturition and its effects on the conceptus have been investigated in The Gambia, West Africa. Malarious placentae occurred in 1300 (20.2%) of 6427 singleton births, in 32 (18.6%) of 172 sets of twins and in none of six sets of triplets. Plasmodium falciparum infections predominated; P. malariae or P. ovale infections were found in only nine instances. In the large group of single births placental malaria occurred less frequently (12.0%) in residents of urban than of other, more rural, communities (27.1%). In the former group incidence showed no clear change with season; in the latter group it was highest in the trimester following the end of the rains and lowest in the second half of the dry season. In both residential groups it was more frequent in primiparae (urban 16.1%; other 46.9%) than in multiparae (urban 8.9%; other 20.3%). The sex of the child did not influence malaria incidence. Dense placental infections were more frequent in primiparae. Stillbirth rates of singleton infants were significantly higher for males than for females, but no clear and consistent relationship between stillbirth and placental malaria was detected. Mean singleton birthweights were depressed by about 170 g in the presence of malaria; the deficits were statistically significant only among first born infants and tended to diminish progressively with increasing maternal parity. No distinct gradient linking birthweight with ascending density of placental parasitaemia was observed. Singleton birthweights of 2.5 kg or less occurred more frequently in association with malarious than non-malarious placentae and the association was more marked among first born than later birth rank infants. Differences between the weights of malarious and non-malarious placentae were small and not significant. The findings of the study are discussed in relation to the widely prevalent view that pregnancy exacerbates maternal malaria by attenuating acquired immunity.