Influence of the shortened warming protocol on human blastocyst viability: an in-vitro experimental study

Does the shortened warming protocol impact the cell viability and outgrowth competence of human vitrified blastocysts warmed with or without fatty acids?

In this study, 326 discarded vitrified human blastocysts donated for research by consenting couples were used. The blastocysts were randomly allocated to five groups depending on the warming solutions, protocols and recovery culture media: the control-conventional, control-shortened, FA-conventional, FA-shortened, and FA-shortened/recovery culture with fatty acid (FA-shortened/RF) groups. The blastocysts were warmed with or without fatty acids following the manufacturer's instruction (conventional method) or using the shortened method, in which blastocysts were immersed in a thawing solution for 1 min and then cultured in the recovery medium for 2 h. The embryo volume recovery, cell viability, intracytoplasmic lipid droplets and outgrowth competence were evaluated.

The degree of blastocyst volume recovery was significantly higher after shortened warming than after conventional warming (P = 0.0130-0.0278). Cell membrane collapse was observed during the shortened warming. The blastocyst survival rate and expansion status after the recovery culture were comparable among the five groups. However, the proportion of necrotic cells was increased in the control-shortened, FA-shortened and FA-shortened/RF groups (P = 0.0160-0.0498). The adhesion rates were comparable among all the groups; however, the outgrowth area was significantly higher in the FA-conventional group than in the other groups at 96 h (P = 0.0026-0.0487).

The efficacy of the shortened warming protocol depends on the warming solutions used. The shortened protocol effectively improves the daily workflow; however, to prioritize clinical outcomes, each laboratory should thoroughly examine its impact before introducing it.