Introduction: It is estimated that about 140 million people worldwide are exposed to arsenic levels in drinking water above the WHO's suggested limit of 10 μg/L. Exposure during pregnancy has been associated with low birth weight, preterm birth, small for gestational age (SGA), etc. In Peru, the province of Tacna has shown considerable concentrations of arsenic in drinking water. Objective: The aim of this study is to assess the effect of arsenic consumption in drinking water on perinatal outcomes in Tacna province. Methods: A longitudinal observational study was carried out in which 150 pregnant women were recruited up to the 24th week of pregnancy. A drinking water sample from their most consumed source was collected for the analysis of total inorganic arsenic, and a urine sample for the evaluation of total urinary arsenic and its different metabolites (U-iAsIII, U-iAsV, arsenobetaine...