Journal of Clinical Medicine
Comparison of Modified Natural Cycle Versus True Natural Cycle Frozen Embryo Transfer in Terms of Clinical Pregnancy and Live Birth Outcomes: A Single-Centre Retrospective Cohort Study
By Gonca Yetkin Yıldırım, İpek Uzaldı, Tuba Varlı Yelke and 1 others.
Abstract
Objectives
Natural cycle frozen embryo transfer (FET) has become an increasingly preferred approach for endometrial preparation in ovulatory women. Whether modified natural cycle (mNC) protocols incorporating human chorionic gonadotropin (hCG) for ovulation triggering provide any reproductive advantage over true natural cycle (tNC) protocols remains controversial. This study aimed to compare pregnancy and live birth outcomes between mNC-FET and tNC-FET cycles.
Methods
This retrospective cohort study analysed 256 frozen–thawed embryo transfer cycles in ovulatory women at a single tertiary centre between January 2014 and December 2024. Of these, 91 cycles used an mNC protocol (mNC-FET group) and 165 cycles used a tNC protocol (tNC-FET group). All transfers involved a single day-5 good-quality or top-quality blastocyst, with identical luteal phase support. Baseline demographic and clinical characteristics, ovarian reserve markers, and embryological parameters were compared between groups. Multivariable logistic regression was performed to identify independent predictors of live birth.