Pyrethroid pesticide exposure, malaria, and birth size in a ghanaian cohort

Pyrethroid pesticides are widely used in sub-Saharan Africa for malaria vector control, as the predominant insecticide in treated bednets, or as a chemical during indoor residual spraying campaigns. In non-malarious areas, prenatal pyrethroid exposure has been negatively associated with newborn size, although effect sizes have been typically small, and results inconsistent. We aimed to evaluate the association of urinary prenatal pyrethroid concentrations on newborn size in an area where malaria is endemic and accounts for significant reductions in birth size. Within a prospective Ghanaian prenatal cohort (GRAPHS), we measured pyrethroid insecticide metabolites in repeated urine samples across pregnancy. With multivariable linear regression, we examined associations between creatinine-corrected pyrethroid metabolite concentrations averaged over pregnancy and birth weight, length, and head circumference and examined effect modification by placental malaria. Models were adjusted for other pesticide co-exposures (organophosphate, herbicide metabolites) and other potential confounders such as parity, BMI, wealth, and cook smoke exposure. Among samples from 1,152 pregnant GRAPHS participants, 90% had detectable 3-phenoxybenzoic acid, OPM, a metabolite of pyrethroids commonly used for malaria control (permethrin, cypermethrin, deltamethrin). Median OPM prenatal exposure was 0.36 μg/mL (IQR 0.17, 0.84). A doubling of OPM was associated with a -19.1 gram (95% CI: -39.7, 1.4) decrease in birth weight. Among participants who had placental malaria, a doubling of OPM was associated with a -0.6 cm (95% CI: -0.9, -0.3) decrease in birth length. No association between OPM and head circumference was identified. Pyrethroids are negatively associated with infant size at birth, even in a malarious area where use is aimed at reducing the incidence of pregnancy malaria. This finding, along with increasing pyrethroid resistance among Anopheles mosquitoes, underscores the imperative to identify and test alternative malaria control strategies for use in pregnancy.