Repeated freezing and thawing impacts IVF outcomes in PGT-A cycles

Researchers in a 2021 study found reduced live birth rates when embryos were frozen before biopsying for PGT-A was performed.

In some cases of PGT-A, blastocysts are frozen without biopsy, then thawed at a later date to perform the procedure.

Aluko et al. (2021) tested whether or not these repeated freeze and thaw cycles are harmful to the embryo, in the context of PGT-A/PGS testing.

This study also looked at the impact of rebiopsying embryos (embryos that had been biopsied, then frozen, then thawed, then biopsied a second time – often due to getting a “no result” from the first biopsy). Unfortunately this was a very small sample size (15) and they weren’t able to do any kind of meaningful statistical analysis.

Check my complete guide to PGT-A to get more background on PGT-A (aka PGS testing).

Results

A total of 2713 FET cycles were included:

• 2603 cycles in group BC (biopsied, then cryopreserved)
• 95 cycles in group CBC (cryopreserved, then biopsied, then re-cryopreserved)
• 15 cycles in group BCBC (biopsied, then cryopreserved, then rebiopsied, then re-cryopreserved)

They looked at embryo survival after the first thaw:

• 98.2% survived in group BC
• 94.6% survived in group CBC
• 93.3% survived in group BCBC

Then looked at survival after the second thaw:

• 98.9% survived in group CBC
• 100% survived in group BCBC (small sample size: only 15 in this group)

The pregnancy rates were higher in group BC vs CBC (72.5% vs 57.9%), as well as the live birth rates (55.1% vs 28.4%).

There were no differences in miscarriages in group BC and CBC.

In addition, they calculated risk ratios and controlled for age, number of oocytes retrieved, prior miscarriage, day of embryo freezing, number of previous cycles, reason for IVF, and embryo quality. They found that these adjusted risk ratios for clinical pregnancy rate (0.67) and live birth rate (0.57) were significantly lower between group BC and CBC. This means that the pregnancy rate was 33% lower in group CBC compared to group BC (and 43% lower for live birth).

Note that this isn’t an absolute reduction in pregnancy or live birth rate, but a % decrease. So if the live birth rate was 50% then 43% lower is 28.5%, not 3%.

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Conclusions

Clinical pregnancies and live birth rates in PGS/PGT-A cycles were higher when the embryo was only frozen a single time.

Although this study attempted to measure a difference from the once biopsied group (BC) to the twice biopsied group (BCBC), they were unable to draw meaningful conclusions because of the small sample size.

Reference

Aluko A, Vaughan DA, Modest AM, Penzias AS, Hacker MR, Thornton K, Sakkas D. Multiple cryopreservation-warming cycles, coupled with blastocyst biopsy, negatively affect IVF outcomes. Reprod Biomed Online. 2021 Mar;42(3):572-578. doi: 10.1016/j.rbmo.2020.11.019. Epub 2020 Nov 29. PMID: 33516664; PMCID: PMC10036156.

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About Embryoman

Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.

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