Compared to repeated oocyte retrieval procedure, frozen-thawed embryo transfer (FET) has been widely used to increase the cumulative pregnancy rate per IVF-cycle, with demonstrated superiority in preventing ovarian hyperstimulation syndrome and improving cost-efficiency and time to pregnancy.~It is controversial whether triggering ovulation of the dominant follicle using human chorionic gonadotrophin (hCG) may benefit or reduce embryo implantation, when compared with a natural cycle environment. Unfavourable clinical outcomes of controlled ovarian stimulation have been reported by recently published studies, compared to the spontaneous LH surge.~This study aimed to compare the effectiveness in terms of better clinical pregnancy rates (CPR) of pure natural cycle frozen-thawed embryo transfer (NC-FET) versus natural cycle frozen-thawed embryo transfer modified by HCG administration\with hCG-triggered ovulation (mNC-FET).~A retrospective analysis was conducted between 2012-2017. In patients with regular ovulatory cycles, the timing of embryo thawing and transferring was based on spontaneous LH surge (NC-FET). Patients attended for ultrasound evaluation of the dominant follicle from Day 8 to 10 of their menstrual cycle (depending on cycle length), detecting luteinizing hormone (LH) surge in urine/ taking an ovulation test for urinary LH measurement. In selected cases, a serum assays of LH, progesterone and estradioI has been further obtained. When the endometrial thickness reached 8 mm and dominant follicle 16-20 mm in diameter, hCG was administered in absence of urinary LH surge. Embryo thawing and transfer was planned 7 days after LH surge or HCG administration, whether G5 or G6 blastocyst. Exogenous progesterone supplementation started 2 days after hCG administration versus the same day of embryo transfer procedure in NC- ET. To limit potential confounders, only single blastocyst transfer cycles were included, vitrified on Days 5 or 6, excluding PGT-a (Pre Gestational Test for aneuploydia) cycles and cleavage stage embryo transfers. A unilevel and multi level logistic regression analysis was conducted using Stata Software versione15.
In recent years, frozen-thawed embryo transfer procedure (FET) has been widely used to increase the cumulative pregnancy rate per IVF-cycle: which is the best preparation protocol remains a matter of debate.~A retrospective analysis was conducted between 2012-2017. The aim was comparing clinical pregnancy rate (CPR) of pure natural cycle frozen-thawed embryo transfer (NC-FET) versus natural cycle frozen-thawed embryo transfer with hCG-triggered ovulation (mNC-FET).