High pressure frozen oocytes have improved ultrastructure but reduced cleavage rates compared to conventionally fixed or vitrified oocytes

Context Live birth rates are lower for cryopreserved oocytes than for fresh IVF cycles, indicating a need for improved methodologies. Aims The aim of this study was to determine if high pressure freezing (HPF) could improve both ultrastructural preservation and cryopreserved oocyte quality when compared to conventional fixation and vitrification methods. Methods Sheep oocytes and embryos were prepared by HPF or vitrification, with or without cryoprotectants. Frozen oocytes were prepared for transmission electron microscopy or warmed, in vitro fertilised and the recovery and cleavage rates recorded. Key results Blastocyst rates were similar between fresh, HPF and vitrified embryos. HPF oocytes had improved ultrastructure compared to conventional fixation or vitrification, but had poorer survival and cleavage rates compared to vitrified oocytes. Freeze-substitution of cryopreserved oocytes and transmission electron microscopy demonstrated disruption of the oocyte ultrastructure in the presence of cryoprotectants. Conclusions Superior preservation of ultrastructure was observed in HPF oocytes compared to vitrification or conventional fixation methods. In the presence of CP, both embryos and oocytes could survive HPF and warming but oocytes had reduced development. Implications The HPF method has potential to be developed and lead to improved oocyte and embryo cryopreservation and outcomes for assisted reproduction.

O-008 Low grade blastocysts result in healthy live births and should not be discarded

Study question

Does transfer of low grade blastocysts results in acceptable live birth rates the birth of healthy babies?

Summary answer

While BC/CB/CC blastocysts have a reduced chance of live birth compared with AA/AB/BA/BB blastocysts, the absolute chances are still reasonable.

What is known already

Transfer of poorer quality embryos and blastocysts result in lower live birth rates, though to what extent is unclear, nor if there is an absolute threshold below which live births are very rare or even do not occur. Further, the developmental competence of the inner cell mass (ICM) or trophectoderm (TE) could at least theoretically impact the pregnancy and/or the health of the baby. Many clinics do not transfer or freeze poor quality embryos and blastocysts, and prefer to submit the patient to a further stimulation cycle.

Study design, size, duration

We performed a retrospective analysis of 10,978 couples undergoing singleton blastocyst transfers between 2009 and March 2020. We included all single blastocyst transfers for which there was complete data on blastocyst quality, singleton or twin births, birthweight and gestation at delivery, irrespective of blastocyst grading, female age, cause of infertility, ovarian response or endometrial thickness. We recorded live birth rates, birth weight and gestational age.

Participants/materials, setting, methods

Data from 14 clinics in 3 countries, 8 from China, 5 from New Zealand, and 1 from Australia were included in the final dataset. We compared the impact of blastocyst grading using multiple logistic regression. Blastocyst grading was based on the Gardner classification, in which the first letter denotes the grade of the inner cell mass (A is best), and the second letter the grade of the trophectoderm.

Main results and the role of chance

Overall, 10,978 single blastocyst cycles resulted in 4,261 live births (38.8%) (4195 singletons and 132 twins). Live birth rates were 47% after transfer of AA blastocysts (n = 2306); 42% after AB/BA (n = 2088); 33% after BC (n = 1973); 25% after CB (n = 715) and 14% after CC (n = 117). There were too few AC (n = 27) or CA (n = 12) blastocysts to include in the analysis. The odds of live birth for BC/CB/CC blastocysts compared with AA/AB/BA blastocysts, vary between 0.8 and 0.9.

The live birth rate appears to be more dependent on ICM quality (C grade, n = 844, 23.2%) rather than TE quality (C grade, n = 2117, 32.1%), with the odds of live birth 0.43 and 0.57 respectively compared to A grade ICM or TE.

The average birth weight (singleton only) was 3336.9+/-570.3 g (range 3323 to 3386 g), and the average gestation at delivery (singleton only) was 38+6+/-2.0 weeks (range 38+2 to 39+1). There was no significant difference for birth weight or gestational age at delivery between blastocysts of different grades.

Limitations, reasons for caution

This was a retrospective study. Grading was based on inner cell mass and trophectoderm and not on degree of expansion, or on day of transfer.

It is likely that higher quality blastocysts were transferred first, in a fresh cycle, and poorer quality blastocysts frozen for later transfer.

Wider implications of the findings

The most important finding is that reasonable live birth rates are obtained in CC-blastocysts.

We therefore advocate that CC-blastocysts should be replaced or frozen for later transfer. It is reassuring that there was no impact of blastocyst quality on birth weights or gestational age at the time of delivery.

Trial registration number

Not applicable

P–138 When is low quality really low? Should we transfer low-grade blastocysts?

Study question

What is the live birth rate after single, low-grade blastocyst (LGB) transfer?

Summary answer

The live birth rate for LGBs is 28%, ranging between 15–31% for the different inner cell mass (ICM) and trophectoderm (TE) subgroups of LGBs.

What is known already

Live birth rates following LGB transfer are varied and have been reported to be in the range of 5–39%. However, these estimates are inaccurate as studies investigating live birth rates following LGB transfer are inherently limited by sample size (n = 10–440 for LGB transfers) due to LGBs being ranked last for transfer. Further, these studies are heterogenous with varied LGB definitions and design. Collating LGB live birth data from multiple clinics is warranted to obtain sufficient numbers of LGB transfers to establish reliable live birth rates, and to allow for delineation of different LGB subgroups, including blastocyst age and female age.

Study design, size, duration

We performed a multicentre, multinational retrospective cohort study in 9 IVF centres in China and New Zealand from 2012 to 2019. We studied the outcome of 6966 single blastocyst transfer cycles on days 5–7 (fresh and frozen) according to blastocyst grade, including 875 transfers from LGBs (<3bb, this being the threshold typically applied to LGB studies). Blastocysts with expansion stage 1 or 2 (early blastocysts) were excluded.

Participants/materials, setting, methods

The main outcome measured was live birth rate. Blastocysts were grouped according to quality grade: good-grade blastocysts (GGBs; n = 3849, aa, ab and ba), moderate-grade blastocysts (MGBs; n = 2242, bb) and LGBs (n = 875, ac, ca, bc, cb and cc) and live birth rates compared using the Pearson Chi-squared test. A logistic regression analysis explored the relationship between blastocyst grade and live birth after adjustment for the confounders: clinic, female age, expansion stage, and blastocyst age.

Main results and the role of chance

The live birth rates for GGBs, MGBs and LGBs were 45%, 36% and 28% respectively (p < 0.0001). Within the LGB group, the highest live birth rates were for grade c TE (30%) and the lowest were for grade c ICM (19%). The lowest combined grade (cc) maintained a 15% live birth rate (n = 7/48). After accounting for confounding factors, including female age and blastocyst characteristics, the odds of live birth were 2.33 (95% CI = 1.88–2.89) for GGBs compared to LGBs and 1.56 (95% CI = 1.28–1.92) for MGBs compared to LGBs following fresh and frozen blastocyst transfers (p < 0.0001, odds ratios confirmed in exclusively frozen blastocyst transfer cycles). When stratified by individual ICM and TE grade, the odds of live birth according to ICM grade were 1.31 (a versus b; 95% CI = 1.15–1.48), 2.82 (a versus c; 95% CI = 1.91–4.18) and 2.16 (b versus c; 95% CI = 1.48–3.16; all p < 0.0001). The odds of live birth according to TE grade were 1.33 (a versus b; 95% CI = 1.17–1.50, p < 0.0001), 1.85 (a versus c; 95% CI = 1.45–2.34, p < 0.0001) and 1.39 (b versus c; 95% CI = 1.12–1.73, p = 0.0024).

Limitations, reasons for caution

Despite the large multicentre design of the study, analyses of transfers occurring within the smallest subsets of the LGB group were limited by sample size. The study was not randomised and had a retrospective character.

Wider implications of the findings: LGBs maintain satisfactory live birth rates (averaging 28%) in the general IVF population. Even those in the lowest grading tier maintain modest live birth rates (15%; cc). It is recommended that LGBs not be universally discarded, and instead considered for subsequent frozen embryo transfer to maximize cumulative live birth rates.

Trial registration number

Not applicable

P–167 Assuring quality in embryology decision making: blastocyst grading agreement assessed via a smartphone application

Study question

Given the subjectivity of blastocyst grading and the challenge of performing routine competency assessments, how consistently do embryologists grade blastocysts when using an easily accessible phone application?

Summary answer

Grading agreement was fair to moderate for inner cell mass (ICM) and trophectoderm (TE), evidence that a mobile application can be used for quality assurance.

What is known already

Embryologists routinely perform external quality assessments (EQA), though the utility of EQA for quality improvement is limited, and more active, user-friendly tools are needed to improve quality assurance in embryology. Blastocyst grading is one of the most important and subjective tasks in clinical embryology, important for both blastocyst ranking and decision to freeze. Inter-user agreement is only fair for ICM (kappa 0.349) and TE grade (kappa 0.397; Storr et al., 2017). Fair agreement has also been reported for decision to freeze for a cohort of blastocysts that exhibited borderline morphology (kappa 0.301; Hammond et al., 2020).

Study design, size, duration

A prospective study of blastocyst grading consistency using ARTCompass, a mobile phone application designed to assess clinical decision making of laboratory staff for andrology and embryology competency. Two assessments, each with 100 images of expanded blastocysts in three planes, were performed by 42 embryologists from 9 clinics in 2 countries between April to July 2020. Survey 1 assessed ICM grading and survey 2 assessed TE grading using the same set of images for consistency.

Participants/materials, setting, methods

Blastocysts were of proportionally mixed grades (ranging from grade A to X) using a modified Gardner system that included “X” for non-viable ICM/TE. Embryologists were advised to complete the tests individually in one sitting. The Fleiss kappa coefficient (k) measured inter-rater agreement among embryologists when assigning blastocyst grade. Kappa value interpretation is as follows <0.20: poor; 0.21–0.40: fair; 0.41–0.60: moderate; 0.61–0.80: good and 0.81–1.00: very good.

Main results and the role of chance

Overall, agreement for ICM and TE grades was moderate among embryologists (kappa 0.47, 0.52, respectively). ICM grade B and C had the lowest agreement (0.37, 0.39), while ICM grade X (no, or degenerate ICM), and TE grade A showed the highest agreement (0.68, 0.62). These results illustrate that embryologists had difficultly classifying ICM grade when it was of moderate to poor quality (grade b or c), likely due to subjectivity in grading size and compaction level, but were good at classifying ICM grade when there was no apparent ICM (grade x). For TE grade, embryologists consistently identified a top-quality TE (grade a), which is reassuring as TE grade is the primary morphological feature used for blastocyst ranking. In general, this QA platform offers ease of use and shows agreement values for ICM and TE that are similar to other studies, suggesting that blastocyst grading with a mobile phone application is a viable option for quality assurance.

Limitations, reasons for caution

Only blastocyst grading was assessed, therefore additional competency assessments using a mobile device should be assessed for accuracy. Further studies are needed to determine if mobile applications can improve competency.

Wider implications of the findings: Ease of use by 42 embryologists indicates mobile applications may provide a user-friendly and accessible platform for QA. Since effective and efficient assessment of competency and KPIs is an ongoing challenge for laboratories, a mobile application is a novel and effective tool to monitor QA parameters in the IVF laboratory

Trial registration number

Not applicable