A nomogram to assist blastocyst selection in vitrified-warmed embryo transfer cycles

The purpose of the study was to establish a mathematical model to help rank the order of blastocysts and assist selection of which blastocysts to warm in vitrified-thawed embryo transfer cycles.

A total of 2862 women who underwent first vitrified-thawed single blastocyst transfer (SBT) between July 2015 and July 2019 were retrospectively recruited and randomized into a training set (n = 2289) and testing set (n = 573). Least absolute shrinkage and selection operator (LASSO) regression was used to screen the factors critical to live birth (LB). Subsequently, a nomogram model was established to convert the effect of each factor on LB into a measurable score. The efficacy of the model was then evaluated by the receiver operating characteristic and calibration curve. The performance of the model was also internally tested in the testing set.

Maternal age, endometrial thickness, oocyte number, day-3 embryo quality, blastocyst morphology, and blastulation day were selected as the critical predictors of LB in the vitrified-thawed SBT cycle and fitted into a nomogram model. The area under the curve (AUC) of the model was 0.67, and the AUC in the testing set was 0.64, which indicates moderate discrimination. The calibration curve showed good concordance between prediction and observation. Importantly, the score of each variable in the nomogram helped to rank the order of the blastocysts resulting in LB.

The nomogram model can provide guidance for embryo selection in vitrified-thawed blastocyst transfer cycles, which may help to optimize the LB rate.