Résumé
Background: In sub-Saharan Africa, malaria in the first half of pregnancy is harmful for both the mother and her foetus. However, malaria in the 1st trimester of pregnancy, when women are usually not protected against malaria, has been little investigated. For the first time, we assessed the effects of malaria in the 1st trimester on maternal and birth outcomes using a preconceptional study design. Methods: From June 2014 to March 2017, 1214 women of reproductive age were recruited and followed monthly until 411 became pregnant. Pregnant women were then followed from 5-6 weeks of gestation until delivery. Path analysis was used to assess the direct effect (i.e., not mediated by malaria in the 2nd or 3rd trimester) of malaria in the 1st trimester on maternal anaemia and poor birth outcomes. The cumulative effect of infections during pregnancy on the same outcomes was also evaluated. Results: The prevalence of malaria infection in the 1st trimester was 21.8%. Malaria in the 1st trimester was significantly associated with maternal anaemia in the 3rd trimester (adjusted odds ratio [aOR]: 2.25, 95% CI 1.11, 4.55). While we did not evidence any direct effect of 1st trimester malaria infections on birth outcomes, their association with infections later in pregnancy tended to increase the risk of low birthweight. Conclusions : alaria infections in the 1st trimester were highly prevalent and have deleterious effects on maternal anaemia. They highlight the need for additional preventive measures starting in early pregnancy, or even before conception.