Post-warming degree of blastocoel re-expansion is the best prognosticator for live birth rates in vitrified-warmed single blastocyst transfer cycles

Abstract

Recent studies have presented contradictory results regarding significance of Inner-cell-mass (ICM)/Trophectoderm (TE) gradation and degree of blastocoel expansion/re-expansion for increased live-birth rates. Also, few studies have reported combined results from fresh/frozen and single/double transfer cycles. This study aimed at individually assessing the relevance of grades of ICM, TE and degree of post-warm blastocoel re-expansion on live-birth rates exclusively in vitrified-warmed single-blastocyst transfer cycles. Retrospective study (n=216) vitrified-warmed elective single blastocyst transfer cycles. Oocyte donation, Embryo-donation, assisted hatching and preimplantation genetic diagnosis cycles were excluded. All blastocysts were graded as per Gardner and Schoolcraft method of classification as 1-6 for degree of expansion and grades A/B/C for ICM and TE. Natural-cycle endometrial preparation with hormone supplementation followed by luteal-phase support with micronized progesterone. Endometrial response was noted by ultrasound. Single blastocyst-transfer was done 3 hours after warming of vitrified blastocyst. Warmed blastocyst was compared with pre-vitrified blastocyst for degree of expansion, gradation of ICM/TE. β-hCG level measured on day8 of transfer indicated pregnancy. Live-birth was the primary outcome measure. Women were classified into Live-birth (LB; n=74) and non-pregnant (NP; n=142) groups. Age, BMI, infertility period, number of oocytes retrieved, rate of formation of good quality cleavage-stage and blastocyst-stage embryos and survival rates post-warming did not differ significantly between the two groups. Same brand of embryo-transfer catheter and same brand and volume of media was used for transfer. However, degree of re-expansion was significantly higher in LB group than in NP group (Mean ± SD: 3.6 ± 1.0 v 3.2 ± 0.94, P=0.0068). The Fisher-Exact test odds-ratio for achieving a live-birth with 3-4 degree of re-expansion was 2.78 (p=0.0016) whereas the odds ratio was much lower (0.36) with any other degree of re-expansion. Although ICM grade was higher/better in Live-birth group than in non-pregnant group, the difference remained statistically non-significant (Odds ratio 1.25, p=0.82). No significant difference was observed in TE grades between the two study groups (p=0.17). A notable difference was also observed in endometrial echopattern (p=0.03) although the endometrial thickness remained comparable between the groups. Thus, post-warming degree of re-expansion is the single most promising predictive factor for live birth rates in such cycles. Re-expansion of blastocoel to an expanded grade 3/4 is superior to ICM and TE cell gradation for better live-birth rates in vitrified-warmed single blastocyst transfer cycles. However, larger multicentric trials may be required to establish it as robust predictor of live-birth.