The effect of timing and frequency of Plasmodium falciparum infection during pregnancy on the risk of low birth weight and maternal anemia

Plasmodium falciparum infection during pregnancy causes maternal anemia and low birth weight (LBW), but the effect of frequency and timing of infection on the severity of these adverse effects is unknown. We conducted a cohort study recruiting 2462 pregnant women in Malawi. Microscopy was used to diagnose malaria at enrollment, follow-up and delivery. Birth weight and maternal hemoglobin were measured at delivery. The association between timing and frequency of infection and LBW and maternal anemia was analyzed using a binomial regression model. Compared with uninfected women, (i) the risk of LBW increased with the number of malaria episodes [one episode: prevalence ratio (PR) 1.62 (95% CI 1.07–2.46); two episodes: PR 2.41 (95% CI 1.39–4.18)]; (ii) the risk for maternal anemia increased with the number of malaria episodes [one episode: PR 1.15 (95% CI 0.86–1.54); two episodes: PR 1.82 (95% CI 1.28–2.62)]; and (iii) the risk of LBW was higher with infection in the second (PR 1.71; 95% CI 1.06–2.74) than third trimester or at delivery (PR 1.55; 95% CI 0.88–2.75). The timing and frequency of P. falciparum infection during pregnancy affected the risk of LBW but only frequency of infection had an effect on the risk of maternal anemia. Identification of gestational periods when malaria causes most adverse outcomes will facilitate effective targeting of interventions.