Background. Genetic polymorphisms could interact with disinfection by-products metabolism and increase their toxicity which may result in an increased risk of intrauterine growth restriction (IUGR). Aim. To evaluate whether the single nucleotide polymorphism (SNP) rs3813867 (G1259C) of CYP2E1 gene modifies the relationship between IUGR and trihalomethanes (THMs) exposure during pregnancy as previously reported by Infante-Rivard (2004).