Urinary arsenic species and birth outcomes in Tacna, Peru, 2019: a prospective cohort study.

Arsenic exposure during pregnancy might affect foetal development. Arsenic metabolism may modulate the potential damage to the fetus. Tacna has the highest arsenic exposure levels in Peru. However, this region also has the highest birth weight in Peru. It is not known if arsenic exposure is affecting maternal-perinatal health in Tacna. This study aimed to evaluate the association between urinary arsenic metabolism and birth outcomes, specifically birth weight and gestational age at birth in Tacna, Peru. A prospective cohort study was conducted, involving 158 pregnant women in Tacna, Peru, during January-November 2019. Participants were enrolled in their second trimester and followed-up until birth. Urine samples were collected in the second and third trimesters. Urine samples were analysed for total arsenic concentration and its species. Generalised estimating equations analysis was used to evaluate the association of interest. Inter-differences in arsenic toxicokinetics, calculated with principal component analysis was included as an interaction term. Analysis was stratified by pregnancy trimester. The median total urinary arsenic concentration was 33.34 μg/L. Inorganic arsenic and dimethylarsinic acid were higher in the second trimester. Dimethylarsinic acid was the predominant component (84.78% of total urinary arsenic). No significant association was found between urinary arsenic exposure and birth weight or gestational age at birth. The association was not affected by arsenic metabolism. Stratified analyses by pregnancy trimester also showed no significant associations. Urinary arsenic was not associated with birth weight, and this null relationship remained unaffected by arsenic toxicokinetic differences reflected in urine.