BackgroundAntiviral intervention in hepatitis B virus (HBV)-infected pregnant women can effectively reduce mother-to-child transmission. However, the immunological characteristics of pregnant women with chronic HBV infection and the effects of antiviral intervention during pregnancy on maternal immune response remain unknown. We aimed to investigate these effects by comparing mothers who received antiviral intervention during pregnancy with those who did not.MethodsPregnant women positive for hepatitis B surface antigen and hepatitis B e-antigen (HBsAg+HBeAg+) were enrolled at delivery, including 34 received prophylactic antiviral intervention during pregnancy (AVI mothers) and 15 did not (NAVI mothers). T lymphocyte phenotypes and functions were analysed using flow cytometry.ResultsAt delivery, maternal regulatory T cell (Treg) frequency in AVI mothers was significantly higher than that in NAVI mothers (P< 0.002), and CD4+T cells in AVI mothers displayed a decreased ability to secrete IFN-γ (P= 0.005) and IL-21 (P= 0.043), but an increased ability to secrete IL-10 and IL-4 (P= 0.040 andP= 0.036), which represented a higher Treg frequency, enhanced Th2 response and suppressed Th1 response. Treg frequency among AVI mothers was correlated negatively with serum HBsAg and HBeAg levels. After delivery, the ability of CD4+T cells or CD8+T cells to secrete IFN-γ or IL-10 was similar and no significant difference in Treg frequency was found between the two groups.ConclusionsProphylactic antiviral intervention during pregnancy has an effect on T cell immunity in pregnant women, which was characterised by increased maternal Treg frequency, enhanced Th2 response and suppressed Th1 response at delivery.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12884-023-05700-8.