2339

Background: The province of Tacna, Peru, presents arsenic levels in drinking water above the WHO suggested limit of 10µg/L. One of the adverse effects during pregnancy is the increased rate of small for gestational age (SGA). However, comparing to the rest of Peru, SGA in Tacna is lower but large for gestational age (LGA) is the highest in all the country. Here we have evaluated the water and urinary arsenic metabolites in pregnant women and their association with birth outcomes.Methods: We estimated the arsenic concentration in drinking water and urine during the second and third trimester of pregnancy in 150 women that live in Tacna from February to July,2019. Water arsenic was evaluated qualitatively, and urinary arsenic (tAs, As^III, As^V, MMA and DMA) was quantified by HPLC-MS. Primary ((MMA+DMA)/tAs) and Secondary (DMA/(MMA+DMA)) methylation-indexes (PMI/SMI) were generated. Reproductive outcomes were assessed as tertiles of exposure. Results: We found an almost even distribution of arsenic exposure in drinking water (30.43% to ≤10µg/L; and 34.78% for 25µg/L and 34.78% for ≥50µg/L). Mean total urinary arsenic was higher according to the exposure group (38.08, 51.86 and 65.38ng/mL, respectively). It is appreciated an increase of SGA proportion by tertile of total urinary arsenic (tAs) (2.38%, 7.32% and 8.57%) although not significantly. On the other hand, the proportion of LGA is reduced when increasing the tertile of %As^V: 38.1%, 35,8% and 28.57%, respectively. Conclusions: Although no significant relationship was found between arsenic exposure and births outcomes, there is a tendency of higher risk of SGA with increasing tertile of tAs. On the other, according to recent research, the aymara ethnic population, Tacna’s main ethnicity, is characterized by high birthweights for gestational age, and our results show that higher %As^V might shift this normal pattern, reducing the proportion of LGA; nonetheless, greater sample size is required.