Article
Blasts from the past: is morphology useful in PGT-A tested and untested frozen embryo transfers?

https://doi.org/10.1016/j.rbmo.2020.07.014Get rights and content

Abstract

Research question

Day of cryopreservation, inner cell mass (ICM) grade, trophectoderm grade and blastocyst expansion grade have been associated with differences in live birth rate in frozen embryo transfer (FET) cycles. This study sought to examine the likelihood of live birth and whether the morphological grade of the blastocyst is more or equally useful in FET cycles among preimplantation genetic testing for aneuploidies (PGT-A) tested and untested blastocysts.

Design

This was a retrospective cohort study of 6271 vitrified-warmed, autologous, single-embryo transfer cycles among patients undergoing IVF from July 2013 to December 2017 at a single, university-affiliated infertility practice. The primary outcome was live birth, calculated by generalized estimating equations.

Results

Among PGT-A tested embryos, inferior ICM grade was associated with a lower chance of live birth (ICM grade B versus A: adjusted risk ratio [aRR] 0.91, 95% confidence interval [CI] 0.84–0.99). Among untested blastocysts there was a lower live birth rate in blastocysts cryopreserved on day 6 versus day 5 (aRR 0.87, 95% CI 0.78–0.96), and those with inferior pre-vitrification trophectoderm grade (trophectoderm grade B versus A: aRR 0.86, 95% CI 0.79–0.94). Blastocysts with a higher pre-vitrification expansion grade (pre-vitrification expansion grade 5 versus 4: aRR 1.1, 95% CI 1.01–1.2) were associated, but ICM grade was not associated (ICM grade B versus A: aRR 0.93, 95% CI 0.86–1.02), with chance of live birth.

Conclusions

Among PGT-A untested blastocysts, assessing embryo quality by day of cryopreservation, trophectoderm grade and expansion grade may help to identify embryos with the highest likelihood of live birth. Identifying euploid embryos by PGT-A appears to homogenize the cohort, making blastocyst morphological grade and day of cryopreservation less important.

Introduction

Vitrification and advances in embryo culture conditions have closed the historical gap in live birth rate between frozen embryo transfer (FET) and fresh embryo transfer cycles (Chen et al., 2016; Roque et al., 2013; Wong et al., 2017). FET largely eliminates the risk of ovarian hyperstimulation syndrome and has been associated with a lower incidence of ectopic pregnancy, preterm birth and low birthweight (Ishihara et al., 2011; Maheshwari et al., 2018; Sha et al., 2018). While fresh embryos encounter a variably stimulated endometrium, vitrified-warmed embryos benefit from a more physiological uterine environment, thereby allowing for managed synchronization with the window of implantation through endometrial programming (Casper and Yanushpolsky, 2016). FET also allows for preimplantation genetic testing for aneuploidies (PGT-A) via trophectoderm biopsy without time constraints to obtain a result. In addition, data suggest that an elevated serum progesterone concentration on the day of triggering is detrimental to fresh cycle outcomes (Bosch et al., 2010; Venetis et al., 2013). For these reasons and others, some clinicians advocate a ‘freeze-all’ strategy, culturing embryos and vitrifying them with or without trophectoderm biopsy after they reach the mature blastocyst stage (Basile and Garcia-Velasco, 2016).

The advent of single-embryo transfer, in the setting of multiple available frozen blastocysts, has led to the clinical conundrum of which blastocyst to transfer first. From an available cohort of frozen blastocysts, many characteristics have been proposed to select those of the highest quality and with the maximum chance of a live birth. Blastocyst morphological grade remains the most commonly used criterion for blastocyst selection. Some retrospective studies suggest that blastocysts vitrified on culture day 5 may have improved clinical outcomes, including a higher live birth rate, compared with those vitrified on day 6 (Ferreux et al., 2018; Wang et al., 2016). A systematic review and meta-analysis from 2010 found a higher live birth rate in day 5 versus day 6 frozen blastocysts; however, slow freezing was used in 8 out of 9 studies. When limited to studies that used vitrification, the ongoing pregnancy and live birth rates for day 5 and day 6 blastocysts were comparable (Sunkara et al., 2010). A 2011 study by Ahlström and colleagues investigated the influence of blastocoele expansion and trophectoderm and inner cell mass (ICM) grades on clinical outcomes in FET. They found that trophectoderm grade was the strongest indicator of success (Ahlström et al. 2011). In contrast, Du and co-workers’ similar retrospective analysis suggested that degree of blastocoele expansion was the morphological parameter best associated with live birth (Du et al., 2016). Attention also has been given to trophectoderm morphology and embryonic progression, with some evidence of improved clinical pregnancy and live birth rates among faster growing embryos and those with higher grade trophectoderm morphology (Ahlström et al., 2011; Cimadomo et al., 2018; Irani et al., 2018; Kaing et al., 2018; Kroener et al., 2012; Rienzi et al., 2019). These observations support a growing body of literature suggesting that the morphological grade of blastocysts may be a better indicator than day of vitrification alone. However, these data have largely been limited to PGT-A untested blastocysts.

Recent studies have shown significantly higher live birth rates and lower miscarriage rates in select populations when transferring vitrified-warmed blastocysts deemed euploid by PGT-A (Chen et al., 2015; Irani et al., 2018; Forman et al., 2013). Blastocyst biopsy for PGT-A is not thought to impair the reproductive potential, and is not associated with a reduction in live birth (Scott et al., 2013). It is also well accepted that although morphology and aneuploidy are linked at the blastocyst stage, the association is weak, and consequently morphological analysis cannot be relied on to ensure transfer of chromosomally normal blastocysts (Alfarawati et al., 2011). On a daily basis, clinicians and patients are faced with selecting a single blastocyst from a frozen cohort, whether PGT-A tested or untested. This study sought to identify characteristics of cryopreserved blastocysts that were associated with the highest likelihood of live birth in FET cycles and to examine whether blastocyst morphology is more useful in PGT-A tested compared with untested blastocyst transfers.

Section snippets

Inclusion criteria

This was a retrospective cohort study of patients who underwent autologous IVF or intracytoplasmic sperm injection (ICSI) cycles at a single university-affiliated infertility practice and had an oocyte retrieval from 1 July 2013 to 31 December 2017. For each oocyte retrieval, all of the subsequent single-embryo transfer cycles with embryos that were cultured to blastocyst stage and vitrified were included. If PGT-A was performed, cleavage-stage biopsy was excluded, and only those that underwent

Results

During the study period, 6271 FET met the inclusion criteria. These blastocysts were retrieved in 4761 cycles from a total of 4338 patients. Of the blastocysts transferred, 2478 (40%) were deemed euploid by PGT-A, and 3793 (60%) were untested (Table 1). The group that had undergone PGT-A testing had a median maternal age at transfer of 36.2 years versus 33.7 years for the group with PGT-A untested blastocysts. There was a lower proportion of diagnosis of unexplained infertility among the PGT-A

Discussion

Among PGT-A untested blastocysts, the model indicates that assessment of blastocyst quality by day of vitrification, trophectoderm grade and expansion grade may help to identify blastocysts with the highest likelihood of live birth in FET cycles. Among blastocysts deemed euploid by PGT-A, however, the cohort appears to be homogenized, making blastocyst morphological grade and the day of cryopreservation less important for blastocyst selection.

Embryonic progression, day of cryopreservation,

Acknowledgements

This work was conducted with support from Harvard Catalyst | The Harvard Clinical and Translational Science Center (National Center for Research Resources and the National Center for Advancing Translational Sciences, National Institutes of Health Award UL1 TR001102) and financial contributions from Harvard University and its affiliated academic health care centres. The funding sources had no involvement in the study design, collection, analysis or interpretation of data, the writing of the

Matthew A. Shear MD is a Resident Physician in Obstetrics and Gynecology at Beth Israel Deaconess Medical Center and a Clinical Fellow in Obstetrics, Gynecology, and Reproductive Biology at Harvard Medical School, Boston, USA.

Key message

Clinicians and patients have no clear guide when selecting a vitrified-warmed blastocyst for transfer. Among PGT-A untested blastocysts, morphology, day of cryopreservation and expansion grade all associate with live birth. Among PGT-A tested

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    Matthew A. Shear MD is a Resident Physician in Obstetrics and Gynecology at Beth Israel Deaconess Medical Center and a Clinical Fellow in Obstetrics, Gynecology, and Reproductive Biology at Harvard Medical School, Boston, USA.

    Key message

    Clinicians and patients have no clear guide when selecting a vitrified-warmed blastocyst for transfer. Among PGT-A untested blastocysts, morphology, day of cryopreservation and expansion grade all associate with live birth. Among PGT-A tested embryos deemed euploid, these associations are attenuated and less important.

    These authors should be regarded as joint first authors.

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