Nomogram to Predict an Endometrial Thickness >7.5 mm in the Frozen Embryo Transfer Cycle for Thin Endometrial Women

Abstract Background A sufficient endometrial thickness (EMT) is essential for successful pregnancy. For patients with a thin endometrium (EMT ≤7.5 mm on human chorionic gonadotropin [HCG] trigger day) in IVF, some studies have suggested freezing all embryos and preparing the endometrium in the subsequent frozen-thawed cycle, but not all patients can obtain a thicker endometrium during endometrial preparation in the frozen embryo transfer cycle than on HCG trigger day in the fresh embryo transfer cycle. This study aimed to investigate which characteristics of patients with a thin endometrium suggest the possibility of EMT >7.5 mm in the subsequent frozen cycle, and build up a prediction nomogram. Methods Data were collected from the university-based reproductive medical center between January 2013 and September 2019. Multivariable logistic regression was used to generate the final prediction model and construct the nomogram. Model performances were quantified by discrimination and calibration. Results The predictive variables that entered the final model were: hysteroscopic adhesiolysis history, PCOS status, application of clomiphene in the ovarian stimulation process, the ovarian stimulation protocol, and the endometrial preparation protocol. The receiver operating characteristic curve for the final model and validation cohort was 0.76 (95% confidence interval [CI]: 0.722–0.797) and 0.71 (95% CI: 0.66–0.76), respectively. Discrimination performed well in both the modeling and validation cohorts. Conclusion We conclude that in women with a thin endometrium (EMT ≤7.5 mm on HCG trigger day), the absence of a hysteroscopic adhesiolysis history, and the presence of PCOS, the application of clomiphene in the ovarian stimulation process, the application of a GnRH agonist short protocol, mild stimulation protocol, natural cycle protocol, and natural cycle for endometrial preparation are prognostic for an increased possibility of EMT >7.5 mm in the subsequent frozen cycle.