Submicroscopic Plasmodium falciparum Infections Are Associated With Maternal Anemia, Premature Births, and Low Birth Weight

Background. Molecular, as opposed to microscopic, detection measures the real prevalence of Plasmodium falciparum infections. Such occult infections are common during pregnancy but their impact on pregnancy outcomes is unclear. We performed a longitudinal study to describe that impact. Methods. In a cohort of 1037 Beninese pregnant women, we used ultrasound to accurately estimate gestational ages. Infection with P. falciparum, hemoglobin concentration, use of intermittent preventive treatment during pregnancy (IPTp) for malaria, and other parameters were recorded during pregnancy. Using multivariate analyses, we evaluated the impact of submicroscopic infections on maternal anemia, premature birth, and low birth weight. Results. At inclusion, polymerase chain reaction (PCR) and microscopy detected infection in 40% and 16% of women, respectively. The proportion infected declined markedly after 2 doses of IPTp but rebounded to 34% (by PCR) at delivery. Submicroscopic infections during pregnancy were associated with lower mean hemoglobin irrespective of gravidity, and with increased anemia risk in primigravidae (odds ratio [OR], 2.23; 95% confidence interval [CI], .98-5.07). Prospectively, submicroscopic infections at inclusion were associated with significantly increased risks of low birth weight in primigravidae (OR, 6.09; 95% CI, 1.16-31.95) and premature births in multigravidae (OR, 2.25; 95% CI, 1.13-4.46). Conclusions. In this detailed longitudinal study, we document the deleterious impact of submicroscopic P. falciparum parasitemia during pregnancy on multiple pregnancy outcomes. Parasitemia occurs frequently during pregnancy, but routine microscopic and rapid diagnostic tests fail to detect the vast majority of episodes. Our findings imply caution in any revision of the current strategies for prevention of pregnancy-associated malaria.