P–211 Double warming and double vitrification for euploid embryos does not affect implantation nor ongoing pregnancy rate
Authors: Hashimi B A 
Published: August 2021

Abstract

Study question
Does exposure of embryos to double vitrification and double warming affect the chances of ongoing pregnancy for patients undergoing PGT-A and transfer euploid embryos?

Summary answer
Our analysis shows that there is no statistically significant difference in implantation or ongoing pregnancy rate between single or double vitrification/warming cycles.

What is known already
The use of PGT-A is increasing in the last years and progressively more patients opting in for this, in order to reduce time to pregnancy. Implantation failures prior to genetic testing or the incidence of no-result embryos post PGT-A are some of the scenarios that expose the embryos to multiple rounds of vitrification/warming cycles. The exact effect that such exposure has on embryos is still to be investigated and confirmed as to whether it affects the outcome (i.e. implantation/ongoing pregnancy rate) or the future health of the child.

Study design, size, duration
Our analysis is a retrospective observation study of data collected from 151 consecutive frozen euploid embryo transfers (FET). These were performed at a single centre between January-December 2020. Two groups were created for this study. The first group includes euploid embryos that were transferred post being exposed to single vitrification/warming (n = 126). In the second group euploid embryos were exposed twice to vitrification/warming (n = 25). Statistical analysis using chi-square test and statistical significance was calculated when p ≤ 0.05.

Participants/materials, setting, methods
Blastocysts from 151 patients were split into two groups based on the number of vitrification/warming cycles that they underwent prior to FET. The first group includes embryos that were subjected to trophectoderm biopsy and were then vitrified (n = 126). The second group includes embryos that were initially vitrified without undergoing PGT-A analysis. Following implantation failures, their remaining embryos were warmed, biopsied and re-vitrified. Post PGT-A analysis euploid embryos were then re-warmed and transferred (n = 25).

Main results and the role of chance
For the first group (A), 450 blastocysts (day 5–7) were subjected to trophectoderm biopsy, where 5-cells taken, and embryos were then vitrified. Post PGT-A analysis 260 euploid embryos identified. From them 126 embryos transferred in frozen replacement cycles, where the mean embryo age for the group was 36.1±4.2. The grade of embryos transferred were of 4BC or better based on Gardner’s grading system. The implantation and ongoing pregnancy rate for this group was 62%.
For the second group (B), 101 blastocysts (day 5–7) warmed, in order to undergo trophectoderm biopsy and were then re-vitrified. Post PGT-A analysis 49 euploid embryos identified. From them, 25 embryos transferred in frozen replacement cycles, where the mean maternal age for the group was 35.05±5.2. The grade of embryos transferred were of similar quality to group A. The implantation and ongoing pregnancy rate for this group was 64%.
Statistical analysis confirmed that there is no statistical difference between the groups (p = 0.74).
In addition, 60% of patients (n = 5) who had double vitrification, double biopsy and double warming have ongoing pregnancy.
In conclusion, for transferrable quality euploid blastocysts, double vitrification has comparable reproductive outcomes as in single vitrification, thereby supporting the efficacy of double vitrification/warming when necessary.

Limitations, reasons for caution
This study uses a small sample size of patients. The data are observational and were retrospectively analysed so unknown confounders could not be assessed. The addition of more cycles and further multivariate analysis, including the child’s health is essential for confirmation of the findings. However, initial results are very reassuring.
Wider implications of the findings: Our study has implications for clinical practice and patient counselling. Especially in patients that they choose to undergo PGT-A with pre-vitrified embryos post implantation failures with non PGT-A tested embryos.

Trial registration number
N/A