Malaria infections during pregnancy can cause adverse birth outcomes, yet many infections are undetected by microscopy. Submicroscopic malaria infections are infections which are below the limit of detection of microscopy but can be detected by sensitive methods like polymerase chain reaction (PCR) and loop-mediated isothermal amplification.
Previously data in this area were scarce, but this new systematic review provides a more detailed global picture. Researchers used aggregated data from 23 studies and 45 datasets, published between 1997 and 2021, from the WWARN Malaria in Pregnancy (MiP) Library.
They found submicroscopic malaria in pregnancy occurred in all malarious regions of the world and was more common than microscopic malaria in most settings. Similar to reports among non-pregnant populations, the proportion of submicroscopic malaria among all malaria infections was higher in Asia and the Americas, where it was more common among non-Plasmodium falciparum malaria species.
This study also explored the relationship between infection and fever and found that submicroscopic malaria was associated with fever in Africa but not in Asia and the Americas. In addition, researchers explored factors associated with submicroscopic malaria by geographic region and found that, among parasitaemic women in Africa, submicroscopic infections were more likely in multigravidae and older women, whereas in Asia and the Americas, only older age was a risk factor.
The study also showed that sulfadoxine-pyrimethamine resistance played a role in increasing the risk of submicroscopic malaria in African cohort studies.
Researchers conclude that malaria control in pregnancy should target both microscopic and submicroscopic infections.