Characteristics of Menstrual Cycle Manipulation With Combined Hormonal Contraception in a University Student Population

Abstract

OBJECTIVE(S): Blastocyst hatching is the final stage of human embryonic development before implantation, although the mechanisms underlying this process remain unknown. We previously demonstrated that human blastocysts developed in vitro show repeated expansion and collapse of blastulation, and that the blastula collapse might be associated with disturbance of the trophectoderm (TE). In addition, analysis of the hatching process by time-lapse cinematography (TLC) showed the collapse of blastulation in some fully expanded human blastocysts resulting in formation of a hatching site in the ZP. This study further investigated the relationship between the collapse of blastulation and the outcome of hatching in human blastocysts using TLC. MATERIALS AND METHOD(S): Surplus frozen/thawed early-stage embryos (n1⁄4131) were used in this study. Embryos were maintained at optimal culturing conditions for up to 5 days and images were recorded digitally every 1 to 5 minutes with an exposure time of 1/20 second. Out of those embryos, 44 that had developed into fully expanded blastocysts with formation of a hatching site in the ZP were further analyzed. RESULT(S): Of the 44 fully expanded blastocysts, 36 (81.8%) completely escaped from the ZP [hatching (+)] and the remaining blastocysts degenerated without hatching [hatching (-)]. The difference in collapse frequencies between hatching (+) and (-) was significant (P<0.05). In the hatching (+) blastocysts from the formation of the hatching site to the completion of escape, 9 (27.3%) showed no blastula collapse, while 17 (51.5%) showed partial collapse, and 7 (21.2%) showed general collapse. The time difference was significant between the no-collapse and general-collapse groups (P<0.05). In contrast, out of 44 fully expanded blastocysts with hatching site, 27 (61.3%) formed the hatching site by retracting the ZP followed by the blastula collapse (inward pattern), while the remaining blastocysts formed the hatching site outwardly by constant expansion of the blastula (outward pattern). CONCLUSION(S): This study demonstrated that blastula collapse had a detrimental effect on the viability of fully expanded blastocysts during the hatching process. That the blastula collapse was caused by a disturbance of the TE strongly suggests that this phenomenon is a negative impact of extended culture in vitro. In addition, the time required for completion of the blastocyst escape was shortest in those showing no collapse. Further investigations using TLC are necessary to elucidate the physiological impact of blastula collapse during hatching with respect to different culturing conditions in vitro and in vivo.