Numerous environmental factors such as smoking habits, alcohol intake, economic and social status, and by-product chlorination present in drinking water can determine adverse pregnancy outcomes like a low weight birth, small for gestational age or preterm delivery. In 1998 the Italian Ministry of University and Scientific Technological Research (MURST) has financed a multicentric study in order to evaluate the association between exposure to by-products chlorination in drinking water during pregnancy and adverse pregnancy outcomes at birth such as preterm delivery and low birth weight. We describe the socio demographics characteristics, personal habits and the health status during pregnancy and exposure to the VOX of 171 women recruited from the Research Unit of Rome and L'Aquila. A case control study with incident cases was performed. Exposure to Chlorination By Products (CBP) and confounding factors for studied outcomes, were assessed by a validated questionnaire. At the same time, collection and analysis of 124 tap water samples were carried out directly at women's home. No association was found between CBPs level and low birth weight or preterm delivery. We found an excess risk statistically significantly between preterm delivery and hypertension (OR = 5.06; IC 95% = 1.70-15.44) an excess risk statistically significantly between low birth weight and smokers (OR = 3.43, IC 95% = 1.15-10.26). The CBPs levels were rather low (range cases = 0.09-6.28 microg/L; range controls = 0.01-6.44 microg/L). The results confirm the literature data and the validity of the epidemiological method adopted. The low CBPs levels, under the Law level, are probably imputable to the good quality of sorgive waters. Considering the CBPs level temporal variability in chlorinated waters, is to be hoped a careful and continues surveillance of the CBPs spike levels for better exposure assessment.