The best timing of vitrification after blastocyst biopsy

What is the correlation between the vitrification timing after biopsy and the following clinical outcomes?

Time is what we want most, but we use worst.

Through preimplantation genetic screening (PGS), couples with the indications of repeated implantation failure, recurrent miscarriage, and advanced maternal age, may select the chromosomally normal embryo to transfer (euploid embryo transfer). On the widely-used PGS platform—aCGH (now has been gradually replaced by next-generation sequencing system), the tested embryos must be vitrified after biopsy to wait for the PGS report release . When should the embryologists vitrify the biopsied embryo? Does the timing of vitrification correlate with the following clinical outcomes?

An information provided by Lee Women's Hospital in 2015 Annual Meeting of Taiwan Society of Reproductive Medicine (2015 TSRM) displayed the clinical outcomes of different vitrification timings after biopsy. A total of 224 cycles were involved, and the biopsy criteria were shown as below:

1. Gardner grading system: Grade of expansion 4, 5, 6

2. Gardner grading system: Inner cell mass(ICM) and Trophectoderm(TE) Grade A or B (AA/AB/BA/BB)

3. Biopsy on Day 5 or Day 6

Table 1. The correlation between the timing of vitrification and embryo expansion before cyropreservation:

Table 2. The correlation between embryo expansion level at vitrification and following clinical outcomes:

*The survival rate of warming embryo =100%。

*The single euploid embyro transfer was performed.

According to Table 2, the implantation rate was higher in Group 4 than Group 1 (p=0.0492), and both the Group 3 and 4 had higher clinical pregnancy rates than that of Group 1 (p=0.009 and p=0.027, respectively). Combining the information in Table 1 and Table 2, vitrification after 3 hrs of biopsy and with over 3/4 expansion displayed better clinical outcomes. Compared those fitted these observations and those did not, both the implantation rate and clinical pregnancy rate could reach significant difference (p=0.01 and p=0.006, respectively).

The above analyses was limited by its retrospective nature (e.g. sample size variation among groups), and it deserved further study to validate the "best timing" of vitrification for the biopsied embryos. More precise the timeline of embryo can be hold, better clinical outcomes may be obtain.