Background/AimsThere is a gap in understanding of whether arsenic exposure during pregnancy alters the maternal immune response and antibody transfer to the infant. We aimed to establish a birth cohort in a region with low-moderate drinking water arsenic concentrations to investigate the relationship between arsenic exposure and immunogenicity of a seasonal quadrivalent inactivated influenza vaccine (IIV) in pregnant women and infants.MethodsWe established a birth cohort (NCT03930017) at the JiVitA Maternal and Child Health and Nutrition Research Project site, which covers ~650,000 people over 500 km2 in rural northern Bangladesh. We planned to enroll 850 pregnancies to achieve a desired sample size of 400 mother-infant pairs at three-months postpartum, based on minimum detectable differences in geometric mean hemagglutination inhibition antibody titers for seasonal quadrivalent IIV antigens when comparing the highest and lowest quartiles of arsenic exposure. From July 2018 to June 2019, we screened women of reproductive age to identify incident pregnancies. Multiparous pregnant women were enrolled in gestational weeks (GW) 13-16. At enrollment, we collected drinking water, urine, blood, and saliva, and administered IIV.ResultsWe screened 52,000 women to identify 2,623 incident pregnancies in multiparous women. Of these, 1,338 were identified prior to GW 16, 846 consented, and 784 enrolled. We followed 567 mother-infant pairs to three-months postpartum. At enrollment, all participants contributed drinking water, urine, blood (processed as plasma, serum, and peripheral blood mononuclear cells), and saliva. An analysis of 40 drinking water samples selected at random found that arsenic concentrations were comparable to arsenic-endemic regions of the U.S. (geometric mean: 3.03 µg/L, geometric standard deviation: 9.54 µg/L, range: 0.05 to 96.83 µg/L).ConclusionsThe number of pregnancies enrolled in our cohort yielded the sample size needed to investigate prespecified aims related to low-moderate arsenic exposure and altered maternal and child immune response.