The blastocyst re-expansion status after thawing do not seem to affect the clinical outcomes in freeze all preimplantation genetic testing (PGT) cycles

Abstract

The integrity and formation of the blastocyst cavity (blastocoel) is maintained by the sodium pump (Na+/K+-ATPase), which gradually increases fluid accumulation and pressure on both TE and zona pellucida (ZP). When the blastocyst collapses after manipulations like biopsy and/or vitrification, the blastocoel gradually re-expands regaining fluid accumulation and pressure on both the TE and ZP. The degree of re-expansion is considered one indicator of the recovery status for frozen blastocysts and some studies have shown that fast re-expanding blastocysts have superior pregnancy rates, while others failed to find any correlation between the re-expansion speed and the implantation rate of frozen blastocysts. Moreover, the dynamics of re-expansion of frozen biopsied blastocyst can be different than blastocysts that were simply collapsed or left intact before freezing. The aim of our study was to determine the implantation rate of euploid frozen blastocyst according to their re-expansion status after different time intervals between the warming and the transfer. Retrospective single center cohort study. Study period: July 2018 – September 2018. Warming time and transfer time were recorded for each FET cycle. Only patients transferring euploid blastocysts of consistent quality were included. Embryos were assessed 3 times: right after, 1h after warming, and right before the transfer. Blastocyst with dark, granular appearing cells and large areas of degeneration were identified as nonsurviving. In terms of re-expansion, blastocyst were classified as Collapsed (C): no sign of re-expansion; Re-Expanding (RE): showing sign of re-expansion; re-Expanded (E): re-expanded at the same grade as before biopsy/freezing; Hatching (H): herniating from the zona pellucida or fully hatched. Patients were divided in 4 groups according to the time interval between the warming and the embryo transfer (< 3h, >3h, <5h, >5h) and matched between the groups <3h and > 3h, and <5h and > 5h for female age (+/-1 year), number of embryo transferred, use of gestational carrier and/or egg donor and day of freezing. Expansion Rate at the transfer, Clinical Pregnancy Rate (CPR), Implantation Rate (IR) and Abortion Rate (AR) were evaluated. Fisher’s exact test was used for statistical analysis. The results are reported in Table 1.Table 1Clinical outcomes according to the re-expansion grade at the different time intervals between embryo warming and transfer.< 3h>3h<5h>5hN° Cycles34987339Average age39,5±6.439,0±5,9ns38,6±6,139,7±6,2nsAverage interval2h14’±32’25’’4h35’±1h7’4’’3h23’±54’18’’6h8’±1h3’59’’∗C=collapsed: no sign of re-expansion; RE= Re-Expanding: showing sign of re-expansion; E= re-Expanded: re-expanded at the same grade as before biopsy/freezing; H= Hatching: herniating from the zona pellucida or fully hatched.C at thawing4 (9,0%)10 (8,0%)7 (8,6%)2 (4,5%)∗C=collapsed: no sign of re-expansion; RE= Re-Expanding: showing sign of re-expansion; E= re-Expanded: re-expanded at the same grade as before biopsy/freezing; H= Hatching: herniating from the zona pellucida or fully hatched.C implanted3/4 (75%)3/10 (30%)ns3/7 (42,8%)1/2ns∗C=collapsed: no sign of re-expansion; RE= Re-Expanding: showing sign of re-expansion; E= re-Expanded: re-expanded at the same grade as before biopsy/freezing; H= Hatching: herniating from the zona pellucida or fully hatched.RE at thawing6 (13,6%)1 (0.8%)5 (6,2%)0∗C=collapsed: no sign of re-expansion; RE= Re-Expanding: showing sign of re-expansion; E= re-Expanded: re-expanded at the same grade as before biopsy/freezing; H= Hatching: herniating from the zona pellucida or fully hatched.RE implanted4/6 (66,7%)1/1ns4/5 (80%)0∗C=collapsed: no sign of re-expansion; RE= Re-Expanding: showing sign of re-expansion; E= re-Expanded: re-expanded at the same grade as before biopsy/freezing; H= Hatching: herniating from the zona pellucida or fully hatched.E at thawing26 (61,4%)55 (44,0%)52 (64,4%)14 (31,8%)∗C=collapsed: no sign of re-expansion; RE= Re-Expanding: showing sign of re-expansion; E= re-Expanded: re-expanded at the same grade as before biopsy/freezing; H= Hatching: herniating from the zona pellucida or fully hatched.E implanted18/26 (69,2%)35/55 (63,6%)ns37/52 (71,2%)9/14 (64,3%)ns∗C=collapsed: no sign of re-expansion; RE= Re-Expanding: showing sign of re-expansion; E= re-Expanded: re-expanded at the same grade as before biopsy/freezing; H= Hatching: herniating from the zona pellucida or fully hatched.H at thawing8 (15,9%)59 (47,2%)17 (21%)28 (63,6%)∗C=collapsed: no sign of re-expansion; RE= Re-Expanding: showing sign of re-expansion; E= re-Expanded: re-expanded at the same grade as before biopsy/freezing; H= Hatching: herniating from the zona pellucida or fully hatched.H implanted5/7 (71,4%)38/59 (64,4%)ns14/17 (82,4%)23/28 (83,1%)nsIR30/44 (68.2%)77/125 (61,6%)ns58/81 (71,6%)33/44 (75,0%)nsCPR27/34 (79.4%)67/98 (68,4%)ns53/73 (72,6%)30/39 (76,9%)nsAR5/30 (16.6%)6/77 (7,8%)ns7/58 (12,0%)1/33 (3%)ns∗ C=collapsed: no sign of re-expansion; RE= Re-Expanding: showing sign of re-expansion; E= re-Expanded: re-expanded at the same grade as before biopsy/freezing; H= Hatching: herniating from the zona pellucida or fully hatched. Open table in a new tab The re-expansion status of the blastocysts at the transfer seems not to be indicative of their implantation potential in any of the time intervals we considered. Since we included only patients with consistent quality euploid embryos, we can infer that the embryo characteristic before the freezing are the most indicative of their implantation potential.