Risk factor for interstitial pregnancy following ipsilateral salpingectomy? A retrospective matched case control study

Background Interstitial pregnancy may still happen even after ipsilateral salpingectomy, resulting in massive hemorrhage. Therefore, the purpose of the study is to identify risk factors associated with interstitial pregnancy following ipsilateral salpingectomy and discuss possible prevention.Methods We conducted a retrospective cohort study in a single, large, university-affiliated hospital. Data of 29 patients diagnosed with interstitial pregnancy following ipsilateral salpingectomy from January 2011 to November 2020 were assigned into the case group (IP group). Whereas there were 6151 patients with intrauterine pregnancy after unilateral salpingectomy in the same period. A sample size of 87 control patients was calculated to achieve statistical power (99.9%) and an alpha of 0.05. The age, BMI and previous salpingectomy side between the two group were adjusted with PSM at a ratio of 1:3. After PSM, 87 intrauterine pregnancy patients were successfully matched to 29 IP patients.Results After PSM, parous women were more common and intrauterine operation was more frequent in the IP group compared with control group (P<0.05). There was only one patient undergoing IVF-ET in the IP group as compared with 29 cases in the control group (3.4% vs. 33.3%, P<0.05). Salpingectomy was performed on 5 patients in the IP group and 4 patients in the control group due to hydrosalpinx (P<0.05). Logistic regression indicated that hydrosalpinx was the high risk factor of interstitial pregnancy following ipsilateral salpingectomy (OR = 8.175).Conclusions Hydrosalpinx appears to be an independent factor contributing to interstitial pregnancy following ipsilateral salpingectomy in subsequent pregnancy.