RESUMEN
INTRODUCTION: Medical treatment is a less invasive alternative to surgical management of missed miscarriage. Studies have shown that pretreatment with mifepristone can increase the complete abortion rate in management of first-trimester missed miscarriage compared with misoprostol alone. Two studies have also shown that pretreatment with letrozole could increase the efficacy compared with misoprostol alone. So far, there is no trial comparing letrozole and mifepristone pretreatment for missed miscarriage. We designed this randomised controlled trial to test the hypothesis that for first-trimester missed miscarriage, letrozole pretreatment is non-inferior to mifepristone pretreatment followed by misoprostol in terms of complete abortion rate. METHODS AND ANALYSIS: This is a prospective open-label non-inferiority randomised controlled trial conducted in a single centre. In total, 294 women diagnosed with first-trimester missed miscarriage opting for medical treatment is recruited with informed consent. They are randomly assigned to receive mifepristone or letrozole pretreatment. In the mifepristone group, each woman takes 200 mg mifepristone orally followed 24-48 hours later by 800 µg misoprostol vaginally. In the letrozole group, each woman takes 10 mg letrozole orally per day for 3 days, followed by 800 µg misoprostol vaginally on the third day of letrozole administration. Follow-up is conducted on days 15 and 42 after misoprostol administration. The primary outcome is the overall complete abortion rate. Secondary outcomes include side effects and complications during the study period. Data will be analysed with both intention-to-treat and per protocol approaches. A p<0.05 will be considered as indicating statistical significance. ETHICS AND DISSEMINATION: Ethics approval has been obtained from the Institutional Review Board of the University of Hong Kong-Shenzhen Hospital with approval number: (2020)166. Findings will be disseminated in a peer-reviewed journal and in national and/or international meetings to guide future practice. TRIAL REGISTRATION NUMBER: ChiCTR2000041480.