Seven Years of Vitrified Blastocyst Transfers: Comparison of 3 Preparation Protocols at a Single ART Center

Introduction: Frozen-thawed embryo transfers (FET) have become a standard practice to increase cumulative pregnancy rates, however, the choice of the best preparation protocol remains a matter of debate. Design: Retrospective analysis of clinical pregnancy (CPR) and live birth rate (LBR) of FET in natural cycles (NC-FET), modified natural cycles with hCG-triggered ovulation (mNC-FET), and hormonal artificial replacement (AR-FET). Materials and Methods: For natural cycles, patients were monitored by ultrasound to evaluate the dominant follicle and by urinary LH kits (NC-FET). When the endometrial thickness reached at least 7 mm and the dominant follicle 16-20 mm, hCG was administered in absence of urinary LH surge (mNC-FET). Embryo thawing and transfer was planned 7 days after LH surge or hCG administration. For the AR-FET, oral estradiol valerate was administered from day 2 of menstrual cycle until endometrial thickness reached at least 7 mm and transfer was planned after 5 days of vaginal progesterone start. Only single vitrified blastocyst transfers were included. Results: In total 2,895 transfers were performed of which 561 (19.4%) carried out with NC-FET, 1,749 (60.4%) with mNC-FET and 585 (20.2%) with AR-FET. CPRs were 32.62, 43.05, and 37.26%, respectively. LBR were 24.06, 33.56, and 25.81%, respectively. A statistically significant (p < 0.001) higher LBR for mNC-FET vs. NC-FET (OR 0.49-0.78) and AR-FET (OR 0.47-0.74) was observed. A higher ectopic pregnancy rate (p = 0.002) was observed in NC-FET (3.28%) than in AR-FET (1.83%) and mNC-FET (0.40%). A higher abortion rate (p = 0.031) in pregnancies <12 weeks was observed in AR-FET (27.52%) than in NC-FET (19.67%) and in mNC-FET (19.39%). At Post hoc analysis only female age (OR 0.91-0.95), antimullerian hormone (AMH) (OR 1.01-1.07) and mNC-FET (OR 1.39-1.98) were statically significant prognostic factors for LBRs. Conclusions: These results demonstrate a superior CPR and LBR following FET in hCG-triggered ovulation cycles compared to NC and AR-FET, a higher ectopic pregnancy rate in NC-FET and a higher abortion rate in pregnancies <12 weeks in AR-FET. However, these data need to be confirmed in randomized and prospective studies before definitive conclusions can be drawn. Clinicaltrials.gov ID: NCT03581422.