To investigate the risk factors of intrauterine hepatitis B virus (HBV) infection and the impact of HBV DNA on the infection.The serum levels of HBsAg, HbsAb, HBeAg, HBeAb, HBcAb and HBV DNA were determined in blood samples from 230 HBsAg-positive pregnant women and their newborns by enzyme-linked immunosorbent assay (ELISA) and fluorescence quantitative PCR (FQ-PCR), respectively. The newborns acquiring HBV infection via intrauterine transmission were selected as the case group and others as the control group. The risk factors for intrauterine HBV infection were analyzed by non-conditional logistic regression model.Six infants were found to be HBsAg-positive, and 18 HBV DNA-positive, and 3 of them were positive for both HBsAg and HBV DNA. The rate of intrauterine HBV infection was 9.6% (22/230). The grade of HBV DNA level was identified as the only risk factor of intrauterine HBV infection by non-conditional logistic regression model, with odds ratio (OR) of 1.57 (95% confidence interval 1.12-2.21). Of the 119 pregnant women positive for HBV DNA, 18 were diagnosed as having intrauterine HBV infection, and the likeliness of the infection significantly increased for a maternal serum HBV DNA level > or =10(7) copies/ml (chi(2)=7.92, P or =10(7) copies/ml, the chance for intrauterine HBV infection can be significantly increased.