Study design and patients
We performed a retrospective cohort study between June 2014 and December 2017 in the Center for Assisted Reproductive Technology of Northwest Women’s and Children’s Hospital, Xi’an, China. All patients were followed-up for one year. This study was approved by the ethics committee of the hospital (number 2018002). As part of the clinical process, all patients signed informed consent before the IVF/FET procedure. Data was extracted from our electronic medical record system.
Women who underwent a first cycle of FET were eligible for the study. Women with polycystic ovarian syndrome (PCOS) or other forms of anovulation, and women in whom the thawed embryo did not survive in the current FET cycle were excluded.