Delayed blastocyst development dose not influence the outcome of vitrified warmed transfer cycles

Abstract

During embryonic culture to the blastocyst stage, there are embryos that are delayed in their speed of development with a low implantation rate. Our objective of this study was to compare the clinical outcome according to the day of embryo freezing (day 5 or 6 following fertilization in vitro) when vitrification was postponed until expanded blastocysts developed. Cohort observational study We retrospectively investigated the vitrified-warmed embryo transfer cycles between Jan 2014 and Dec 2015 in Fertility center of CHA Gangnam medical center . Clinical outcome data consecutive of 1,056 vitrified-warming cycles were analyzed. The mean age of the patient was 35.8 ± 4.4 years. According to the time of the vitrification, embryos were divided into day 5 (1,788 embryos of 772 cycles) and day 6 (594 embryos of 284 cycles) group. Blastocysts were assigned to one of three groups scores according to score of embryos. We compared the clinical outcomes of vitrified-warmed blastocyst stage derived from day 5 and day 6. The mean number of blastocysts transferred per cycle, vitrified and transferred embryo score was not different (1.8 ± 0.5 vs. 1.8 ± 0.3, 9.5±0.8 vs. 9.5±1.0, 9.7±0.4 vs. 9.8±0.7, respectively). The survival rates were comparable between the day 5 and day 6 groups (90.15% vs. 88.68%). The clinical pregnancy and implantation rate (56.08 vs. 41.54%, 40.54% vs.29.46%, P<0.05, respectively) of the day 5 were significantly higher than day 6. The abortion rate was lower in day5 as compared to day 6 (13.16% vs 16.10%) but no significant difference. The pregnancy, implantation and abortion rate of high grade blastocyst vitrified on day 5 and day6 was not different (59.08 vs. 51.34%, 48.32% vs.42.76%, 11.45% vs. 13.45%, respectively). Vitrified-warmed blastocyst stage derived from day 5 was significantly higher evidence for clinical pregnancy rate and implantation rate. But lower evidence for abortion rate were frozen either on day 5 or day 6 but no significant difference. But good quality blastocysts that were vitrified on day 6 had similar developmental potential and pregnancy outcomes compared to those of on day5. Thus, the quality of the blastocysts were an important factor that affected the pregnancy outcomes of the vitrified-warmed transfer cycles.