Abstract: Objective To investigate the factors influencing internal exposure of trihalomethanes(THMs) among pregnant women,and to provide a basis for exposure estimates of disinfection by-products in chlorinated drinking water.Methods A total of 277 pregnant women admitted in a hospital in Wuhan city during July to December 2011 were chosen to complete a questionnaire survey.The levels of the four THMs(chloroform,bromodichloromethane,dibromochloromethane,and bromoform) in blood samples were measured by using headspace solid-phase microextraction gas chromatography.The major factors influencing the internal dose of THMs in pregnancy were analyzed with general linear regression.Results The blood level of chloroform ranged from 13.08 to 480.26 ng/L(median=70.17 ng/L) with a detection rate of 100%.The blood level of bromodichloromethane ranged from undetected level to 38.24 ng/L(median=3.30 ng/L) with a detection rate of 86.6%.The blood level of dibromochloromethane ranged from undetected level to 20.92 ng/L(median=0.48 ng/L) with a detection rate of 27.4%.The blood level of bromoform ranged from undetected level to 78.76 ng/L(median=1.41 ng/L) with a detection rate of 43.7%.The blood level of total trihalomethanes(TTHMs) ranged from 17.04 to 491.42 ng/L(median=84.86 ng/L).Both the levels of chloroform and TTHMs were positively correlated with maternal age(β=0.007,P<0.039; β=0.007,P=0.016) and inversely correlated with drinking boiled water(β=-0.170,P=0.003; β=-0.135,P=0.004).Conclusion Maternal age and boiled water may affect the internal exposure of THMs among pregnant women.