Supernumerary blastocysts available for cryopreservation in fresh IVF cycles: prognostic value for IVF outcomes?

Abstract

Supernumerary blastocysts attained during in vitro fertilization (IVF) cycles are often cryopreserved. We investigate whether the number of supernumerary blastocysts available for cryopreservation serves as a positive prognostic factor for IVF outcomes. Retrospective case-control study. All patients <40 years undergoing IVF with fresh blastocyst transfer between 2004 and 2013 were assessed for inclusion. Patients with > 1 blastocyst available for cryopreservation were considered as “cases” while patients with no supernumerary blastocysts served as “controls.” Demographics, baseline IVF characteristics, and ovarian stimulation parameters of the two groups were compared. Cases were stratified into quartiles based on the number of supernumerary blastocysts available for cryopreservation. Implantation, biochemical, clinical pregnancy, miscarriage and live birth rates were compared between cases and controls, with a further sub-analysis between case quartiles and controls. Odds ratios (OR) for implantation, clinical pregnancy and live births were calculated in both analyses and adjusted for age. 2329 patients underwent fresh blastocyst transfer, of which 1275 and 1054 patients served as cases and controls, respectively. On average 3(2-5) blastocysts were cryopreserved in the former group. Cases were younger [33 (31-34) vs. 36 (32-34); P<0.001] compared to controls. They also had higher anti-müllerian levels [1.96 (1.82-2.39) vs. 1.14 (0.56-1.66) ng/mL; P=0.02], required lesser gonadotropins (1725 vs. 2100 IU; P=0.01), and had more oocytes retrieved (15 vs. 11; P=0.02). The odds of implantation (48.7% vs. 33.9%), clinical pregnancy (58.1 vs. 53.0%), and live birth (54.3% vs. 49.6%) were 1.84, 1.22, and 1.11 times higher, respectively in the cases compared to controls. However, the increased odds were not significant after adjusting for age. Comparison of the 1st, 2nd and 3rd case quartiles with controls revealed 2.09 times higher odds of implantation in the 2nd and 3rd quartiles (P=0.02), with a non-significant trend toward higher clinical pregnancy and live birth rates. Our findings suggest that supernumerary blastocysts available for cryopreservation serve as a positive prognostic factor for IVF outcomes after fresh blastocyst transfer. Specifically, patients with > 3 supernumerary blastocysts have higher odds of implantation compared to controls, suggesting potential benefits of elective single embryo transfer in such patients.Tabled 1Pregnancy Outcomes by QuartilesImplantation RateMiscarriage RateClinical Pregnancy RateLive Birth RateControl33.9%3.42%53%49.6%1st Quartile39.7%3.29%52.9%49.7%2nd Quartile49.7%3.61%59.7%56.1%3rd Quartile51.7%3.33%60%56.7% Open table in a new tab