Objective  To investigate the association between maternal hepatitis B virus (HBV) infection and the risk of preterm delivery in a birth cohort study.

  Methods  We collected the data on 12 186 mother-singleton infant pairs registered at First Affiliated Hospital of Anhui Medical University between January 2011 and December 2014 for a retrospective cohort study on the association between maternal HBV infection and preterm delivery. The puerperae of the cohort were grouped into cases (serum HBV surface antigen positive HBsAg+) and controls (HBsAg negative HBsAg–) based on the results of enzyme-linked immunosorbent assay.

  Results  Of all the puerpaerae studied, 94.78% were controls; 2.97% were the cases being HBV e antigen negative (HBeAg–) and 2.25% were cases being HBeAg positive (HBeAg+). The mean gestational age of the cases was lower than that of the controls and the mean gestational age was the lowest in the HBeAg+ cases. The incidence rate of preterm delivery was 17.13% in the HBeAg– cases and was not significantly differ from that of the controls; but in the HBeAg+ cases, the incidence rate was 24.09% and significantly higher than that (14.66%) in the controls, with an adjusted relative risk adj RR of 1.75 (95% confidence interval 95% CI: 1.25 – 2.41). Compared to the controls, the HBeAg– cases had a significantly increased incidence of early preterm delivery (4.14% vs 2.60%, adj RR = 1.93 95% CI: 1.02 – 3.65); in comparison with the controls, the HBeAg+ cases had a significantly higher incidence of late preterm delivery (19.35% vs. 11.97%, adj RR = 1.74 95% CI: 1.36 – 2.59) and also a significantly higher incidence of early preterm delivery (4.74% vs. 2.69%, adj RR = 2.04 95% CI: 1.17 – 3.56).

  Conclusion  Maternal HBV infection with negative serum HBeAg is associated with an increased risk of early preterm delivery; maternal HBV infection with positive serum HBeAg increases both the risk of early and late preterm delivery.