Drivers of trimester disparities in asymptomatic malaria during pregnancy in Kintampo South District: evidence from an Oaxaca-Blinder decomposition Analysis

BACKGROUND: Asymptomatic malaria in pregnancy (AMiP) remains a major public health challenge with important maternal and neonatal consequences. Despite ongoing malaria control efforts, little is known about trimester-specific disparities in AMiP and the extent to which these differences are explained by socioeconomic, clinical, and environmental factors. Most existing studies have focused on overall malaria burden rather than explaining disparities across gestation. This study examined the determinants of trimester disparities in AMiP in the Kintampo South District of Ghana using Oaxaca-Blinder decomposition. METHODS: A facility-based cross-sectional study was conducted among 462 pregnant women in the Kintampo South District of Ghana. Peripheral blood samples were screened for Plasmodium species using microscopy, while structured questionnaires captured sociodemographic, clinical, and environmental characteristics. Data were analysed with STATA 17 using Oaxaca-Blinder decomposition to partition trimester differences in AMiP into explained(characteristics) and unexplained (coefficients) components. RESULTS: The overall prevalence of AMiP was 13.4%, with a significantly higher burden in the second trimester (χ2 = 10.96, p < 0.001). Plasmodium falciparum accounted for most infections. Oaxaca-Blinder decomposition showed that 73.7% of the trimester disparity in AMiP was explained by differences in observed characteristics (endowments). The major contributors to the explained disparity were suboptimal uptake of intermittent preventive treatment with sulfadoxine-pyrimethamine (IPTp-SP) (71.3%), frequent evening outdoor activity (58.6%), infrequent use of mosquito repellents (50.6%), proximity to overgrown vegetation (42.5%), ≤2 malaria diagnostic tests during antenatal care (ANC) (24.1%), and infrequent iron-folate supplementation (18.4%). Conversely, ownership of long-lasting insecticidal nets (LLINs) reduced the unexplained disparity by 41.9%, highlighting its protective effect. CONCLUSION: Disparities in AMiP across trimesters are primarily driven by modifiable socioeconomic, programmatic, and environmental factors rather than inherent biological differences in gestation. These highlight the need to strengthen the prioritisation of early initiation of ANC and frequent exposure to provider-supervised IPTp-SP uptake. In addition, promoting sustained use of LLINs and repellents, alongside community-level environmental management, is critical to reducing exposure risk. Finally, embedding these targeted interventions within ANC services, supported by coordinated multisectoral efforts, will be essential to reduce trimester-specific inequities and improve maternal health outcomes.