To collapse or not to collapse blastocysts before vitrification? A matched case-control study on single vitrified-warmed blastocyst transfers.

RESEARCH QUESTION: Does laser-induced artificial blastocoel collapse result in better blastocyst cryopreservation survival and a higher live birth rate (LBR) in comparison with intact counterparts? DESIGN: Half of the supernumerary blastocysts from IVF cycles were randomly selected before vitrification for laser-induced artificial collapsing or vitrification in intact form. A matched case-control study of first transfers of single blastocysts artificially collapsed (case) or intact (control) before vitrification was conducted. Controls were matched to cases on a 1:1 ratio by female age, parity, fresh and vitrified cycle protocol, blastocyst age and quality, resulting in 309 case-control pairs. RESULTS: The two groups were comparable in terms of their characteristics. Survival rates in the case and control groups (97.8% and 95.7%; P = 0.133) were comparable, but the optimal survival rate was higher in the case group (78.2% and 69.3%; P = 0.03). Clinical pregnancy rates (38.2% and 35.3%; P = 0.518), miscarriage rates (15.2% and 22%; P = 0.190), LBR per transfer (32.4% and 27.5%; P = 0.221) and LBR per warmed blastocyst (31.6% and 26.3%; P = 0.137) were not statistically different between the case and control groups. No significant difference in preterm births (11.1% versus 15.7%), birthweights (3333 ± 723 g versus 3304 ± 609 g) or sex ratio (49.3% versus 50.7% boys) was observed between the two groups. No major malformations were detected in the study population. CONCLUSIONS: Compared with vitrification of intact blastocysts, collapsed blastocysts resulted in a significantly higher optimal survival rate, and although they resulted in a 5% higher LBR, this was not significant for the chosen sample size. Neonatal outcomes were comparable in the two groups.

Morphometric Protocol for the Objective Assessment of Blastocyst Behavior During Vitrification and Warming Steps.

This article describes the noninvasive method of blastocyst morphometry based on time-lapse microphotography for the accurate monitoring of a blastocyst's volume changing during individual phases before and after vitrification. The method can be useful in searching for the most optimal timing of blastocyst exposure to different concentrations of cryoprotectants by observing blastocyst shrinkage and re-expansion in different pre- and post-vitrification phases. With this methodology, the blastocyst vitrification protocol can be optimized. For a better demonstration of the usefulness of this morphometric method, two different blastocyst preparation protocols for vitrification are compared; one with using an artificial blastocoel collapsing and one without this intervention before vitrification. Both blastocysts' volume changes are followed by time-lapse microphotography and measured by photo-editing software tools. The measurements are taken every 20 seconds in previtrification phases and every 5 minutes in the post-warming period. The changes of the blastocyst dimensions per time unit are presented graphically in line diagrams. The results show a long equilibration previtrification phase in which the intact blastocyst first shrinks and then slowly refills the blastocoel, entering vitrification with a fluid-filled blastocoel. The artificially collapsed blastocyst remains in its shrunken stage through the entire equilibration phase. During the vitrification phase, it also does not change its volume. Since the blastocyst morphometry shows a constant volume of the artificially collapsed blastocysts during the previtrification step, it seems that this stage could be shorter. The described protocol provides many additional comparative parameters of blastocyst behavior during and after cryopreservation on the basis of the speed and intensity of the volume changes, the number of partial blastocoel contractions or total blastocyst collapses, and the time to a total blastocoel re-expansion or the time to hatching.

Artificial blastocoel collapse of human blastocysts before vitrification and its effect on re-expansion after warming - a prospective observational study using time-lapse microscopy.

Vitrified human blastocysts show varied re-expansion capacity after warming. This prospective observational study compared behaviour of artificially collapsed blastocysts (study group patients, n = 69) to that of blastocysts that were vitrified without artificial collapse (control group patients, n = 72). Warmed blastocysts were monitored by time-lapse microscopy and blastocoel re-expansion speed and growth patterns compared between study and control groups. These parameters were also retrospectively compared between blastocysts that resulted in live birth and those that failed. Artificially collapsed blastocysts re-expanded on average 15.01 µm2/min faster than control blastocysts (P = 0.0013). Warmed blastocysts expressed four different patterns of blastocoel growth. The pattern showing contractions at the end of culture was observed to have a lower prevalence in control blastocysts, which coincided with the lower incidence of hatching in this group. Re-expansion speed and prevalence of growth patterns were comparable between blastocysts that did and did not result in a live birth. This was seen in the study and control groups. Despite faster re-expansion and different growth patterns of artificially collapsed blastocysts, live birth rate did not differ between groups. However, this result should be interpreted with caution due to the small sample size and high risk of bias.