In utero exposure is the first point of contact with environmental xenobiotics that may affect the maternal-placental-fetal balance. Considering that maternal pathophysiological changes affect intrauterine development, this pilot study was conducted to address how environmental exposure to organophosphate pesticides (OPs) during pregnancy may contribute to maternal endocrine disruption and disturbed hepatic function. A prospective study was carried out with pregnant women (n=97) living in a rural area of the Rio Negro province where OPs are intensively applied throughout 6 months of the year. Blood samples were obtained and biomarkers of OPs exposure (cholinesterases and β-glucuronidase), cortisol (CT) and progesterone (PG) levels, as well as glycemia, were determined. Parameters of liver injury were assayed by measuring aspartate aminotransferase (AST) and alanine aminotransferase (ALT); liver function was assayed by measuring albumin. Biomonitoring carried out during the pre-spraying period (PreS) and spraying period (SP) showed that the population studied was exposed to OPs, proven by the fact that plasma (PCh) and erythrocyte cholinesterase (AChE) decreased very significantly (p