Background: Malaria in pregnancy causes substantial maternal and infant morbidity-mortality, even at submicroscopic parasite levels. In addition, the presence of polyclonal infections secondary to high parasite genetic diversity is a common finding.
Objectives: To determine the frequency of submicroscopic and/or polyclonal plasmodial infection during pregnancy and to establish their impact on clinical presentation, immunity acquisition, and consequences on mother and gestation product.
Methods: A search on Medline was performed using key words (MeSH): pregnancy, malaria, PCR, microscopy, genotype, and clones. Studies on plasmodial infection diagnosed by microscopy and PCR were selected.
Results: A total of 16 studies were included, all carried out in Africa. The weighted mean (WM) of submicroscopic infection was 36%. According to type of infection (microscopic, submicroscopic or negative), the WM of maternal anemia and low birth weight (LBW) were 51%, 42%, 33%, and 19%, 16%, 11%, respectively. Risks (OR), using the negative group as reference, were: a) for maternal anemia 2.12 in microscopic infection and 1.48 in submicroscopic; b) for LBW 1.89 in microscopic and 1.56 in submicroscopic infection. The WM of polyclonal infection was 75% and the mean number of clones by sample was three.
Conclusions: Submicroscopic and polyclonal P. falciparum infections during pregnancy are very common, but have been little studied and their impact must be assessed in each specific region because they depend on malaria transmission intensity and stability, maternal age and parity, among other variables, which are influenced by environmental and socio-economic conditions of each region.