AIM:To evaluate the safety and efficacy of tenofovir monotherapy in pregnant females resistant to lamivudine or telbivudine.The effect of tenofovir on the fetus was also assessed.METHODS:The clinical data of 17 females were reviewed in this study.Adverse events and pregnancy outcomes from January 1,2011 to June 30,2013 were evaluated in the Department of Gynecology and Obstetrics of BeijingDitan Hospital,Capital Medical University,Beijing,China.These pregnant females developed lamivudine(LAM)-or telbivudine(Ld T)-resistant chronic hepatitis B and received tenofovir(TDF)therapy(300 mg/d),and its curative effect,maternal and perinatal adverse events,fetal growth and development,and neonatal prognosis were evaluated.RESULTS:The median hepatitis B virus(HBV)DNA level in the pregnant females with LAM or Ld T resistance was 5.9(range,4.2-7.2)log10 copies/m L before the initiation of TDF.Ten of these females had abnormal alanine aminotransferase(ALT)levels.The patients were treated with TDF for a median of 24 wk(range,12-40 wk).Fourteen females(82.4%)had an HBV DNA level of<500 copies/m L at the time of delivery.This decrease was statistically significant(P<0.0001).Serum ALT levels were normalized in all subjects with an elevated serum ALT level at baseline(P=0.0003).There were no significant changes in serum creatinine and phosphorus levels during TDF treatment.In addition,no adverse events related to TDF treatment were observed.Seventeen females delivered 17 live infants,and all infants had good Apgar scores.The mean birth weight was 3226.5±331.7 g,and the mean length at birth was 50.4±1.1 cm.The growth and development of the infants was normal at birth,and no infants had birth defects related to TDF treatment.Eleven infants completed HBV vaccination and had no evidence of vertical transmission.CONCLUSION:The use of TDF in pregnant females with chronic HBV and LAM or Ld T resistance was safe and effective. AIM: To evaluate the safety and efficacy of tenofovir monotherapy in pregnant females resistant to lamivudine or telbivudine. The effect of tenofovir on the fetus was also assessed. METHHODS: The clinical data of 17 females were reviewed in this study. Adverse events and pregnancy outcomes from January 1, 2011 to June 30, 2013 were evaluated in the Department of Gynecology and Obstetrics of BeijingDitan Hospital, Capital Medical University, Beijing, China. The pregnant females developed lamivudine (LAM) -or telbivudine (Ld T) -resistant chronic hepatitis B and received tenofovir (TDF) therapy (300 mg / d), and its curative effect, maternal and perinatal adverse events, fetal growth and development, and neonatal prognosis were different .RESULTS: The median hepatitis B virus (HBV) DNA level in the pregnant females with LAM or Ld T resistance was 5.9 (range, 4.2-7.2) log10 copies / m L before the initiation of TDF. Ten of these females had abnormal alanine aminotransferase (ALT) levels. The patients were treated with TDF f or a median of 24 wk (range, 12-40 wk) .Fourteen females (82.4%) had an HBV DNA level of <500 copies / mL at the time of delivery.This decrease was significant (P <0.0001). Serum ALT levels were normalized in all subjects with an elevated serum ALT level at baseline (P = 0.0003). Everyone no significant changes in serum creatinine and phosphorus levels during TDF treatment. Additionally, no adverse events related to TDF treatment were observed. Seventeen females delivered 17 live infants, and all infants had good Apgar scores. The mean birth weight was 3226.5 ± 331.7 g, and the mean length at birth was 50.4 ± 1.1 cm. The growth and development of the infants was normal at birth, and no infants had birth defects related to TDF treatment. Eleven infants completed HBV vaccination and had no evidence of vertical transmission. CONCLUSION: The use of TDF in pregnant females with chronic HBV and LAM or Ld T resistance was safe and effective.