P-267 A continuous culture medium with a lower concentration of lactate has a pronounced effect on the percentage of usable blastocysts on day 5

Study question

Does Continuous Single Culture Medium NX, an embryo culture medium containing 1mM lactate, support increased blastocyst development over high lactate Vitrolife G1/G2 Series sequential culture?

Summary answer

There is a statistically significant increase in day 5 usable blastocysts in low lactate culture medium compared to the one with high lactate medium.

What is known already

Studies have shown that day 5 is the most desirable day to obtain blastocysts that are of an expansion, grade and quality to be utilized for transfer and/or vitrification procedures as those result in the highest success of clinical pregnancy,as compared to day 6/ 7 blastocysts, that do not meet criteria. Moreover, recent studies have indicated that there is an increase in chromosomal correctness of embryos cultured in a 1mM lactate environment as opposed to the higher 6-10mM lactate concentrations that have historically been believed necessary for successful blastocyst culture and resulting pregnancy.

Study design, size, duration

A prospective split sibling oocytes study was performed on 50 ICSI and IMSI cycles from October 2020 through April 2021. Oocytes were divided into the low lactate medium and high lactate gradient medium immediately following ICSI/IMSI and thereafter cultured in those medium until the final day of blastocyst culture. All patient ages were included in the sample population.

Participants/materials, setting, methods

This study was carried out in a private clinic. All patient stimulation protocol information and diagnosis’ were recorded; however, there was no restriction on participation. The endpoint was to analyse the resulting usable blastocyst rates on day 5 and day 6 in both arms of the study, using a denominator of normal 2PN fertilization. If a blastocyst was transferred or cryopreserved on day 5 or day 6, it was determined to be usable.

Main results and the role of chance

The resulting data was stratified not only by day 5 and day 6 usable blastocyst rates but also by patient age. It illustrates a statistically significant improvement in day 5 usable blastocysts for patients <35 in CSCM-NXC vs G1/G2 at 56% and 42%, respectively, a 14% increase (p < .05). The overall day 5 usable blastocyst rate was also statistically significant in CSCM-NXC (47%) as compared to G1/G2 (36%), (p < .05) with all ages considered. Additionally, on day 5, there was a higher percentage of usable blastocysts demonstrated in low lactate vs high in patients aged 35-37 (65% vs 42%, respectively) and 41-42 (41% vs 15%). Statistical significance was reversed in patients <35 on day 6, with G1/G2 having 24% usable blasts and CSCM-NXC 10% (p < .05). Interestingly, though not significant, G1/G2 had an increase in usable blastocyst percentage on day 5 in patients >42 (20% vs 11%), but overall, CSCM-NXC saw an increase in that same age group by 16%.

Limitations, reasons for caution

Though statistical significance was found in this study, a greater number will help to bolster the statistical power of the observations. Additionally, more studies are needed in order to ascertain if low lactate has an effect on the development prior to ICSI and resulting culture.

Wider implications of the findings

The mechanism of action that leads to the successful embryo development in low lactate embryo culture medium is vastly unknown, so further studies are required in order to understand the complexities and the impact of the observations provided.

Trial registration number

not applicable.

P-260 Study of kinetic parameters using KIDscoreTMDay5 version 3.0 in euploid, mosaic and aneuploid blastocysts

Study question

Do kinetic parameters change among euploid, mosaic and aneuploid blastocysts? Is the KIDscoreTMDay5 version 3.0 (KS-5.3) correlated to preimplantation genetic testing for aneuploidies (PGT-A) results?

Summary answer

The KS-5.3 differs in embryo ploidy classes. The analysis of the kinetic variables showed that the aneuploid embryos were significantly slower than euploid and mosaic.

What is known already

Chromosomal abnormalities affect more than 50% of embryos in women with >35 years of age and PGT-A is the best way to predict embryo’s ploidy status decreasing implantation failure and miscarriage. However, this procedure is not always possible due to social or moral issues. So, the use of the non-invasive time lapse monitoring could be helpful to determine the morphokinetic characteristics in the different ploidy classes. KS-5.3 (vitrolife,Sweden) is a scoring model based on morphokinetic data, developed to predict the pregnancy rate of day-5 blastocysts. Recent publications showed differences in kinetic parameters between euploid and aneuploid embryos.

Study design, size, duration

This retrospective study analyzed 728 blastocysts with PGT-A results obtained at Villa Mafalda Clinic from May 2020 to June 2021. Embryos were cultured in EmbryoScope+ time-lapse system (Vitrolife) at 37 °C, 6%CO2, and 5% O2. The PGT-A was performed using next-generation sequence (NGS) technology on the trophectoderm biopsy sample on day 5/6/7. Automatic annotations for division times and quality gradings were performed by senior embryologists and all kinetic values were reported in hours post microinjection.

Participants/materials, setting, methods

728 blastocysts were classified in: (E) euploid (n = 172), (M) mosaicism (n = 171) and (A) aneuploid (n = 385). In this study, they were considered KS-5.3 and the following kinetic variables: the time to reach 2 cells (t2), 3 cells (t3), 4 cells (t4), 5 cells (t5), and the blastocyst formation (TB). Continuous variables were reported as the median and interquartile range (IQR). For the statistical analysis, nonparametric tests were performed and p < 0.05 was considered statistically significant.

Main results and the role of chance

KS5.3 was significantly different between groups [E = 6.6(4.6-7.9) vs M = 5.3(2.9-7.2) vs A = 4.0(2.5-6.6), p < 0.0001]. It was significantly higher in euploid than in mosaic and aneuploid (EvsM p = 0.0007, EvsA p  <0.0001, MvsA p = 0.0077). A significant delay in t2,t3,t4 and tb was showed in aneuploid embryos compared to euploid and mosaic, whereas there was no significant difference between euploid and mosaic: [t2: E = 25.80 (24.56-28.09), M = 25.99 (24.49-28.91), A = 27.02 (25.30-29.47), EvsA p  <0.0001, AvsM p = 0.03, EvsM p = 0.32]; [t3: E = 37.08 (34.74-39.34), M = 36.69 (34.55-40.02), E = 38.45 (35.93-41.14), EvsA p = 0.0003, MvsA p = 0.002, EvsM p >0.99]; [t4: E = 38.28 (35.63-41.19), M = 38.49 (35.47-42.13), A 39.72 (37.25-43.31), EvsA p = 0.0001, MvsA p = 0.02, EvsM p = 0.65]; [tb: E = 107.70 (102.20-114.30), M = 110.10 (103.60-116.80), A = 113.7 (106.80-122.70), EvsA p  <0.0001, MvsA p  <0.0001, EvsM p = 0.42]. As for t5, there were no differences among the groups. Longer cell cycles in aneuploid embryos could be associated with activated DNA repair mechanism or during chromosome segregation. Instead, regarding the mosaics, there was a significant difference with euploid embryos only in KS5.3. The age was similar between euploid and mosaic [E = 36.29 (33.42-39.00) vs M = 36.71 (34.00-39.33) p = 0.99], whereas that was significantly higher in aneuploid embryos [A = 39.11(36.01-42.27), EvsA/EvsM p  <0.0001].

Limitations, reasons for caution

All these findings have to be validated in a larger sample size. Furthermore, for the retrospective nature of this study, there were some confounding factors, such as protocol of stimulation, female age, and malefactor. This research did not consider the importance of every single kinetic parameter.

Wider implications of the findings

A further study is needed to verify if there is a correlation between morphology and ploidy status. This could clarify the difference in KS-5.3 between euploid and mosaic. In order to decrease age bias, we should enlarge the sample size to analyze a subgroup of patients with higher maternal age.

Trial registration number

not applicable

P-165 Which are the determining factors influencing the success rate of egg donation programs with imported vitrified oocytes?

Study question

Which are the determining factors influencing the success rate of egg donation programs with imported vitrified oocytes?

Summary answer

Number of oocytes available after warming, male BMI and semen characteristics are critical parameters influencing reproductive results of oocyte donation programs with imported vitrified oocytes

What is known already

The use of vitrified oocytes from foreign banks and the performance of ICSI using fresh sperm from the recipient's partner is a widely used method of heterologous fertilisation. Recent evidence has questioned the overall effectiveness of this approach: vitrification and warming may reduce the number of oocytes available for insemination, resulting in a lower rate of live births per cycle. Recent studies have attempted to define the right clinical strategy to improve the effectiveness of oocyte vitrification cycles, stressing the importance of the number of imported oocytes (8-9 oocytes) and transfer to the blastocyst stage.

Study design, size, duration

Observational longitudinal cohort study of 431 cycles of oocyte donation conducted between January 2015 and February 2019. A total of 398 couples (mean female age: 43.2 ± 3.5, 28-50 years; mean male age: 44.7 ± 6.1, 28-73 years) underwent an IVF cycle with imported donated vitrified oocytes (mean donor age: 25.2 ± 3.5, 19-34 years). All consecutive oocyte donation cycles conducted at the centre for Reproductive Medicine of the European Hospital in Rome were included.

Participants/materials, setting, methods

In order to assess which factors are associated with the various outcomes, uni-and multi-variable analyses were conducted. In the multivariable analyses, variables that showed a p value<0.1 in the univariable analyses were included in the final model. The results were presented as Odds Ratio (OR). The corresponding 95% Confidence Interval (95% CI) was also exposed. A p value <0.05 was considered statistically significant. All analyses were performed with STATA v16.1 statistical software.

Main results and the role of chance

A univariate analysis was carried out showing that among the demographic characteristics studied, the only one that proved significantly able to influence the outcome of the pregnancy test was male BMI. In 49% of unsuccessful cycles, the male BMI was above 25 (p = 0.03). The correlation is confirmed when comparing cycle outcomes in couples with normal/underweight vs overweight/obese men (p = 0.03). The relationship between female or donor BMI and treatment outcome, however, was not statistically significant. The day on which embryo transfer is performed affects the outcome of the cycle: transferring on day 2 compared to day 5 reduces the probability of clinical pregnancy (ET in day 2= positive clinical pregnancy in 4/16 (25%); ET in day 3= 158/307 (51.4%); ET in day 5=40/67 (59.7%). The relationship between male BMI classes and sperm parameters was studied: the distribution of concentration is different in the 3 BMI groups (p = 0.011); in particular, obese men have a significantly lower concentration than normal-weight men (p = 0.006 after Bonferroni correction). There were no statistically significant differences in volume (P = 0.722), morphology (p = 0.100) and motility (p = 0.179), although there was a downward trend in motility, with a reduction in obese subjects compared to normal weight.

Limitations, reasons for caution

This is an observational study and our findings are in contrast with previous studies which do not show any correlation between male partner BMI categories and reproductive outcomes in egg donation programs.

Wider implications of the findings

Our study shows that the number of oocytes available after warming, male BMI, semen characteristics and blastocyst transfer are critical parameters able to influence the reproductive outcomes of egg donation programs with imported vitrified oocytes.

Trial registration number

Not applicable