What are the novel findings of this work?We have developed a predictive model for methotrexate (MTX) resistance in low-risk gestational trophoblastic neoplasia (GTN) with myometrial invasion, which combines a Doppler marker of tumor vascularity with the International Federation of Gynecology and Obstetrics (FIGO) score, thus improving the predictive power of the latter. What are the clinical implications of this work?The Doppler-based predictive model achieved a specificity of 96.6% and stratified patients with low-risk GTN into low (< 10%), intermediate (10-90%) and high (> 90%) probability of MTX resistance. Thus, it has the potential to guide patient counseling and subsequent management.