Background: Interstitial ectopic pregnancy (IEP) happens when implantation occurs in a special location, the interstitial part, of the fallopian tubes. This condition accounts for 3% of all ectopic pregnancies. When the amniotic sac just develops in the interstitial area of the uterine tube without altering the anatomy of the uterine horn, locating the gestational mass by surgery is difficult. This study aims to assess the efficacy of multi-dose intramuscular injection of MTX in the treatment of IEP in the early stages. Methods: A cross-sectional study was conducted in Hanoi Obstetrics and Gynaecology Hospital from January 2018 to July 2019. The patients were selected under the sampling criteria and treated using intramuscular MTX injection with the dose of 1mg/kg/24 hours on day one. The dose in the following day depended on βhCG concentration. If βhCG concentration increases or decreases by less than 15%, the above treatment will be continued on the next day. The total number of MTX injections is 4 shots. Results: 26 eligible patients
successful treatment rate is 84.62%. βhCG significantly decreased after the third injection. Conclusion: Multi - dose intramuscular MTX injection treatment is an effective and safe treatment option for interstitial ectopic pregnancies in early stages.