Date Published: February 04, 2018
Publisher: The American Society of Tropical Medicine and Hygiene
Author(s): Isha Berry, Patrick Walker, Harry Tagbor, Kalifa Bojang, Sheick Oumar Coulibaly, Kassoum Kayentao, John Williams, Abraham Oduro, Paul Milligan, Daniel Chandramohan, Brian Greenwood, Matthew Cairns.
In malaria-endemic areas, Plasmodium falciparum prevalence is often high in young women because of 1) low use of insecticide-treated nets before their first pregnancy and 2) acquired immunity, meaning infections are asymptomatic and thus untreated. Consequently, a common source of malaria in pregnancy (MiP) may be infected women becoming pregnant, rather than pregnant women becoming infected. In this study, prevalence of infection was determined by microscopy at first antenatal care (ANC) visit in primigravidae and secundigravidae in Ghana, Burkina Faso, Mali, and The Gambia, four countries with strong seasonal variations in transmission. Duration of pregnancy spent in the rainy season and other risk factors for infection were evaluated using multivariable Poisson regression. We found that the overall prevalence of malaria at first ANC was generally high and increased with time spent pregnant during the rainy season: prevalence among those with the longest exposure was 59.7% in Ghana, 56.7% in Burkina Faso, 42.2% in Mali, and 16.8% in Gambia. However, the prevalence was substantial even among women whose entire pregnancy before first ANC had occurred in the dry season: 41.3%, 34.4%, 11.5%, and 7.8%, respectively, in the four countries. In multivariable analysis, risk of infection was also higher among primigravidae, younger women, and those of lower socioeconomic status, independent of seasonality. High prevalence among women without exposure to high transmission during their pregnancy suggests that part of the MiP burden results from long-duration infections, including those acquired preconception. Prevention of malaria before pregnancy is needed to reduce the MiP burden.
Malaria in pregnancy (MiP) is a major public health concern, particularly within sub-Saharan Africa, which shoulders a disproportionately large share of the malaria burden.1–3 Within this region, up to 9.5 million pregnant women were estimated to be at risk of Plasmodium falciparum infection in 2015.4 Infection during pregnancy is not only deleterious to the woman but it also puts her fetus at increased risk of adverse outcomes, such as preterm delivery, low birth weight, and intrauterine growth restriction.5–8 Recommended strategies to prevent and treat MiP include free distribution of nets through antenatal care (ANC) and intermittent preventive treatment (IPTp), which involves providing a dose of sulfadoxine–pyrimethamine (SP) to pregnant women at each ANC visit during the second and third trimesters of their pregnancy.9 However, neither of these interventions takes place until a woman reaches ANC, which can leave her unprotected for almost the first half of her pregnancy. Given the burden of MiP, which in some countries has persisted despite the scaling-up of IPTp and delivery of nets, there remains a need to identify women at greatest risk to inform additional interventions.9,10
In areas of seasonal malaria transmission in Ghana, Burkina Faso, Mali, and The Gambia, the prevalence of malaria infection at the time of first ANC contact in pregnancy was generally high, with two countries having prevalence of infection more than 40% by microscopy. The risk of infection was found to increase markedly as the number of months of pregnancy that had occurred in the rainy season before attending ANC increased, with women whose pregnancies spanned most of the rainy season at the highest risk.
We found a substantial burden of malaria infection at the time of first contact with ANC among primigravid and secundigravid women in West Africa. Although there is evidence of increasing prevalence among women whose pregnancy occurs during the rainy season, even women pregnant at a time of low immediate risk had high rates of parasite carriage, likely due to infections acquired before their pregnancy. Additional strategies are needed to prevent MiP, but for maximum impact, these will need to address infections acquired before pregnancy and carried during the first months of pregnancy before contact with ANC.