Aranda A. P–552 Delayed blastocyst development is associated with a higher risk of aneuploidy in patients of advanced maternal age

Study question

Is delayed blastocyst development, assessed by the day of trophectoderm (TE) biopsy, associated with higher rates of aneuploidy?

Summary answer

Our findings show an association between delayed blastocyst development and poorer prognosis, in terms of euploidy rates, in patients of advanced maternal age.

What is known already

Extended culture of embryos past day 5 of development has become routine practice in all freeze-all cycles, including those applying preimplantation genetic testing for aneuploidies (PGT-A). As healthy live births have been obtained from day 6 and day 7 blastocysts, increasing the pool of embryos available for PGT-A is beneficial, particularly for patients of advanced maternal age who face higher cancellation rates. Nevertheless, the association between delayed blastocyst development and aneuploidy rates remains unclear. As current studies have reported opposing findings, detailed analysis of the chromosomal constitution of slowly developing embryos remains paramount.

Study design, size, duration

Retrospective, international, multicentre cohort study of 4211 patients undergoing preimplantation genetic testing for aneuploidy (PGT-A) from January 2016 to July 2020. We evaluated the chromosomal status of 14757 blastocysts tested using TE biopsy and next generation sequencing (NGS). Both autologous and donation cycles were included in the analysis. Cycles were excluded if they utilised preimplantation genetic testing for monogenic disorders (PGT-M) or preimplantation genetic testing for structural rearrangements (PGT-SR).

Participants/materials, setting, methods

We evaluated euploidy, aneuploidy and mosaicism rates reported in day 5 (n = 9560), day 6 (n = 4753) and day 7 (n = 262) blastocysts, stratified by SART-defined maternal age categories (<35, 35–37, 38–40, 41–42, >42). We further assessed the type and frequency of abnormalities reported in all blastocysts classified as clinically unsuitable, according to the day of biopsy. Finally, we examined the specific chromosomes affected in embryos diagnosed with a single uniform (n = 3882) or single mosaic (n = 518) abnormality.

Main results and the role of chance

The mean maternal age within our patient cohort was 39.9±3.7. Overall, slowly developing blastocysts were significantly more likely to be classified as clinically unsuitable (60.6%) compared to day 5 embryos (55.2%; p < 0.0001). This correlation was also observed when stratified by age, with the exception of the <35 age group (p = 0.25). Markedly, the risk of aneuploidy in slowly developing blastocysts became progressively higher with advancing maternal age (p < 0.0001). We did not observe any significant differences in the types of abnormalities diagnosed in slowly developing embryos compared to day 5 blastocysts. Nevertheless, abnormalities affecting all chromosomes were present at the blastocyst stage. Single trisomies and monosomies were the most frequent across all age groups, and were equally prevalent in day 5, 6 and 7 blastocysts. These most commonly affected chromosomes 16, 22, 21 and 15. We observed no significant differences in the incidence of segmental aneuploidies in relation to the day of biopsy, across all age groups. When considered separately, day 7 blastocysts presented with higher rates of structural aberrations, however low numbers limited statistical power. Finally, delayed blastocyst development was not associated with higher mosaicism rates (p = 0.79). Interestingly, single mosaic trisomies and monosomies were most frequently associated with chromosome 19.

Limitations, reasons for caution

Due to the retrospective nature of the study, full elucidation of all potential confounders may not be possible in all instances. The low number of day 7 blastocysts limited statistical power. As such, the results from day 6 and day 7 embryos were evaluated together.

Wider implications of the findings: Our findings offer an important clinical resource for counselling patients of advanced maternal age. Maternal aging may be associated with a higher incidence of aneuploidy in slowly developing blastocysts. Nevertheless, extended culture increases the pool of biopsiable blastocysts, ultimately improving the chance of having a euploid embryo for transfer.

Trial registration number

NA

O-171 Altered meiotic spindle morphology and composition in in vitro matured oocytes

Study question

How does the meiotic spindle tubulin PTMs of MII oocytes matured in vitro compare to that of MII oocytes matured in vivo?

Summary answer

MII cultured in vitro present detyrosinated tubulin in the spindle microtubules, while MII oocytes matured in vivo do not.

What is known already

A functional spindle is required for chromosomal segregation during meiosis, but the role of tubulin post-translational modifications (PTMs) in spindle meiotic dynamics remains poorly characterized. In contrast with GVs matured in vitro within the cumulus oophorous, in vitro maturation of denuded GVs to the MII stage (GV-MII) is associated with spindle abnormalities, chromosome misalignment and compromised developmental potential. Although aneuploidy rates in GV-MII are not higher than in vivo matured MII, disorganized chromosomes may contribute to compromised developmental potential. However, to date, spindle PTMs morphology of GV-MII has not been compared to that of in vivo cultured MII oocytes.

Study design, size, duration

GV (n = 125), and MII oocytes (n = 24) were retrieved from hormonally stimulated women, aged 20 to 35 years old. GVs were matured to the MII stage in vitro in G-2 PLUS medium for 30h; the maturation rate was 68,2%; the 46 GV-MII oocytes obtained were vitrified, stored, and warmed before fixing and subjecting to immunofluorescent analysis. In vivo matured MII oocytes donated to research were used as controls.

Participants/materials, setting, methods

Women were stimulated using a GnRH antagonist protocol, with GnRH agonist trigger. Trigger criterion was ≥2 follicles ≥18mm; oocytes were harvested 36h later. Spindle microtubules were incubated with antibodies against alpha tubulin and tubulin PTMs (acetylation, tyrosination, polyglutamylation, Δ2-tubulin, and detyrosination); chromosomes were stained with Hoechst 33342 and samples subjected to confocal immunofluorescence microscopy (ZEISS LSM780), with ImageJ software analysis. Differences in spindle morphometric parameters were assessed by non-parametric Kruskal–Wallis and Fisher’s exact tests.

Main results and the role of chance

Qualitatively, Δ2-tubulin, tyrosination and polyglutamylation were similar for both groups. Acetylation was also present in both groups, albeit in different patterns: while in vivo matured MII oocytes showed acetylation at the poles, GV-MII showed a symmetrical distribution of signal intensity, but discontinuous signal on individual microtubule tracts, suggesting apparent islands of acetylation. In contrast, detyrosination was detected in in vivo matured MII oocytes but was absent from GV-MII. Regarding spindle pole morphology, of the four possible phenotypes described in the literature (double flattened and double focused; flattened-focused, focused-flattened, with the first word characterizing the cortex side of the spindle), we observed double flat shaped spindle poles in 86% of GV-MII oocytes (25/29) as opposed to 40.5% (15/37) for the in vivo matured MII oocytes (p = 0.0004, Fisher’s exact test). Further morphometric analysis of the spindle size (maximum projection, major and minor axis length) and the metaphase plate position (proximal to distal ratio, angle) revealed decreased spindle size in GV-MII oocytes (p = 0.019, non parametric Kruskal- Wallis test).

Limitations, reasons for caution

Oocytes retrieved from hyperstimulation cycles could be intrinsically impaired since they failed to mature in vivo. Our conclusions should not be extrapolated to IVM in non-stimulated cycles, as in this model, the cumulus oophorus is a major factor in oocyte maturation and correlation with spindle dynamics has been inferred.

Wider implications of the findings

The metaphase II spindle stability compared to the mitotic or metaphase I meiotic one justifies the presence of PTMs such as acetylation and glutamylation, which are found in stable, long-lived microtubules. The significance of the absence of detyrosinated microtubules in the MII-GV group remains to be determined

Trial registration number

not applicable

Aranda A, Popovic M. P–551 Blastocyst cohort size is not associated with embryo aneuploidy: comprehensive multi-centre data from current preimplantation genetic testing cycles

Study question

Does blastocyst cohort size impact aneuploidy rates, evaluated by next generation sequencing (NGS)?

Summary answer

Embryo aneuploidy rates were independent of blastocyst cohort size across all patient ages.

What is known already

The effects of ovarian response on oocyte and embryo quality remain controversial. Several studies have proposed that a high response to ovarian stimulation may negatively impact oocyte competence. Alternatively, irrespective of maternal age, a poor ovarian response may potentially compromise embryo quality. Using blastocyst cohort size as an indirect measure of ovarian response, previous studies applying array comparative genomic hybridisation (aCGH) have demonstrated that the number of embryos available for biopsy does not impact embryo aneuploidy rates. Nevertheless, these findings remain to be confirmed in a comprehensive cohort, using current approaches for preimplantation genetic testing for aneuploidies (PGT-A).

Study design, size, duration

Retrospective, international, cohort study of 3998 patients from 16 clinics undergoing PGT-A from 2016–2020. We evaluated 11665 blastocysts, tested using trophectoderm (TE) biopsy and next generation sequencing (NGS). To eliminate bias of multiple treatments, we considered only the first PGT-A cycle for all patients. Both autologous and donation cycles were included in the analysis. Cycles were excluded if they utilised preimplantation genetic testing for monogenic disorders (PGT-M) or preimplantation genetic testing for structural rearrangements (PGT-SR).

Participants/materials, setting, methods

We evaluated aneuploidy and mosaicism rates, as well as the proportion of patients who had at least one euploid embryo suitable for transfer. Findings were stratified according to SART-defined maternal age groups, <35 (n = 698/2622 patients/blastocysts), 35–37 (n = 988/3141 patients/blastoycsts), 38–40 (n = 1447/3939 patients/blastocysts), 41–42 (653/1562 patients/blastocysts) and >42 (212/401 patients/blastocysts) and blastoycst cohort size (1–2, 3–5, 6–9 and 10 or more biopsied blastocysts).

Main results and the role of chance

The mean maternal age was 37.0±3.7. The overall embryo aneuploidy rate was 50.6% (5904/11665), while mosaicism was established in 4.0% (469/11665) of blastocysts. As expected, the proportion of aneuploid embryos increased steadily with advancing maternal age (31.8%, 41.5%, 58.4%, 71.2%, 87.8%; p < 0.0001), while mosaicism rates did not vary significantly (p = 0.2). Within each age group, we observed no association between the number of blastocysts biopsied and aneuploidy or mosaicism rates. However, as previously suggested, the chance of having at least one euploid embryo increased linearly with the number of embryos biopsied. We observed that young patients (<35) with 1–2 blastocysts had a 70.4% of having at least one embryo suitable for transfer, which increased to 96.4% and 99.2% with 3–5 and 6–9 blastocysts, respectively. Similar trends were observed in the 36–38 and 39–40 age groups. Patients in the 40–41 age group had a significantly lower chance of having a suitable embryo for transfer. Nevertheless, the chance increased from 27.2% with 1–2 embryos to 61.2% with 3–5 blastocysts. Patients with >10 embryos had at least one euploid embryo in 100% of cases, across all ages. Albeit, the numbers of patients within this category was low, and decreased significantly with advancing maternal age.

Limitations, reasons for caution

While blastocyst cohort size is considered to be an indirect measure of ovarian reserve, the number of oocytes retrieved was not evaluated. Our study only included the first PGT-A cycle for all patients. Subsequent, alterations in stimulation protocols may have resulted in an improved response in some patients.

Wider implications of the findings: The comprehensive nature of the study, based on current PGT-A approaches and a large number of cycles across 16 centres increases clinical confidence in the notion that ovarian response is independent of embryo aneuploidy. Importantly, our findings may serve as a valuable clinical resource to guide patient counselling strategies.

Trial registration number

NA

P–013 Sperm freezing does not affect live birth rates: results from 6,594 cycles in normozoospermic patients

Study question

Does sperm cryopreservation influence the reproductive outcomes of normozoospermic patients undergoing elective ICSI?

Summary answer

After controlling for confounders, the use of cryopreserved semen from normozoospermic patients does not affect pregnancy and live birth rates after ICSI.

What is known already

Sperm cryopreservation with slow freezing is a common practice in ART. While frozen-thawed semen typically presents reduced motility and vitality, its use for ICSI is generally considered adequate in terms of reproductive outcomes. Nevertheless, most studies comparing reproductive outcomes between fresh versus cryopreserved sperm include patients with oligo- and/or asthenozoospermia, where the altered quality of the sample can partially mask the full effect of freezing/thawing. The objective of this study is to ascertain whether ICSI using fresh or cryopreserved semen from normozoospermic patients results in similar fertilization rates and reproductive outcomes.

Study design, size, duration

Retrospective cohort of 6,594 couples undergoing their first elective ICSI cycle between January 2011 and December 2019, using normozoospermic partner semen (fresh or cryopreserved). All cycles involved a fresh embryo transfer, either at cleavage or blastocyst stage. Cycles were divided in 4 groups: fresh semen with partner’s oocytes (FSPO, n = 1.878), cryopreserved semen with partner’s oocytes (CSPO, n = 142), fresh semen with donor oocytes (FSDO, n = 2.413), and cryopreserved semen with donor oocytes (CSDO, n = 2.161).

Participants/materials, setting, methods

A slow freezing protocol using GM501 SpermStore medium (Gynemed, Lensahn) was used for all sperm cryopreservation. Sperm washing, capacitation, and selection prior to ICSI were performed equally for fresh and frozen-thawed samples, using pellet swim-up in IVF® medium (Vitrolife, Göteborg). Fertilization rate (FR), pregnancy (biochemical, clinical, and ongoing) and live birth (LB) rates were compared among study groups using Pearson’s Chi square and Student’s t-test. A p-value <0.05 was considered statistically significant.

Main results and the role of chance

Male and female age, sperm concentration and motility after ejaculation, and number of oocytes inseminated were similar between study groups compared (FSPO vs. CSPO, FSDO vs. CSDO). As expected, oocyte donation cycles resulted in higher LB rate than cycles in which partner’s oocytes were used (30.04% vs 18.17%, p < 0.001). In cycles using partner’s oocytes, no significant differences were observed between fresh and cryopreserved sperm in FR, pregnancy and LB rates (p > 0.05 for all outcomes). However, in oocyte donation, the mean FR after ICSI using cryopreserved semen (73.6 ± 19.6) was lower than the FR obtained with fresh semen (75.1 ± 19.2), p = 0.010. Similarly, in oocyte donation cycles, the biochemical pregnancy rate was significantly lower when using cryopreserved semen (48.5% in CSDO vs. 52.3% in FSDO, p = 0.009), while clinical, ongoing pregnancy and LB rates were similar between both semen status (p > 0.05). In oocyte donation, a subgroup analysis including only the ICSI cycles with embryo transfer at blastocyst stage (n = 1.187 for FSDO, n = 337 for CSDO) confirmed that the LB rate was comparable between fresh and cryopreserved semen groups (34.7% vs 35.6% respectively, p = 0.76), without significant differences in pregnancy rates neither (p > 0.05 for all outcomes).

Limitations, reasons for caution

Caution should be exerted when extrapolating these results to different protocols for sperm cryopreservation and selection, or to IVM and classical IVF cycles, which were excluded from analysis. Due to the retrospective nature of the study, some uncontrolled for variables may affect the results.

Wider implications of the findings: Sperm cryopreservation does not affect pregnancy and live birth rates in normozoospermic patients, although it may lower slightly fertilization rates. In line with previous studies including patients with an apparent male factor detected after routine semen analysis, sperm cryopreservation is a safe and convenient technique.

Trial registration number

Not applicable

Canto M, Guglielmo MC, Garcia D, Ponti ED, Marca AL, Vassena R, Buratini J. P–093 The use of donor sperm improves post-ICSI live birth rates in advanced maternal age women

Study question

Can the use of donor sperm improve post-ICSI live birth rate in advanced maternal age (AMA) patients?

Summary answer

The use of donor sperm increases post-ICSI live birth rate while substantially reducing abortion occurrence in AMA patients.

What is known already

Oocyte DNA repair capacity decreases with maternal age, when sperm DNA integrity is particularly important to avoid the transfer of gene truncations and de novo mutations to the zygote. Optimal DNA repair activity in the zygote requires paternal inheritance of 8-oxoguanine DNA glycosylase (OGG1), a rate-limiting enzyme in the base excision repair pathway. However, the involvement of paternal aging and sperm quality in the severe drop in fertility observed in AMA patients has not been addressed. While strategies to mitigate the impact of AMA on fertility have exclusively targeted oocyte quality, the sperm contribution in this scenario remains somehow neglected.

Study design, size, duration

Retrospective, multicentric, international study including 755 first ICSI cycles with patients’ own oocytes achieving a fresh ET between 2015 and 2019, 337 of which using normozoospermic partner semen and 418 using donor sperm. The association of sperm origin (partner vs. donor) with live birth was assessed by univariate/multivariate analysis in non-AMA (<37 years, n = 278) and AMA (≥37 years, n = 477) patients. ICSI outcomes were compared between partner and donor sperm in non-AMA and AMA patients.

Participants/materials, setting, methods

The study was conducted in 3 fertility clinics including 755 Caucasian patients aged 24 to 42 years. Univariate/multivariate analyses were performed to test the association of sperm origin with live birth; infertility factor, maternal age, oocyte yield and number of embryos transferred were included in the model as confounding variables. In addition, ICSI outcomes were compared between donor and partner sperm groups with the Chi-square (percentages) or with the Wilcoxon sum rank (continuous variables) tests.

Main results and the role of chance

The multivariate analysis revealed that the use of donor sperm was positively and independently associated with live birth occurrence in AMA [1.82 OR (1.08–3.07) 95% IC; p = 0.024], but not in non-AMA patients [1.53 (0.94–2.51); p = 0.090]. Maternal age [0.75 (0.64–0.87); p < 0.001], number of MII oocytes recovered [1.14 (1.05–1.23); p = 0.001] and number of embryos transferred [1.90 (1.27–2.86); p = 0.002] were also independently associated with live birth in AMA patients. Live birth and delivery rates were 70–75% higher, while miscarriage rate was less than half in donor sperm compared to partner sperm AMA cycles (LBR: 25.4% vs. 14.5%, p = 0.003; DR: 22.5% vs. 13.5%, p = 0.008; MR: 18.0% vs. 39.5%; p = 0.009). Implantation (17.4% vs. 13.5%; p = 0.075) and clinical pregnancy rates (27.5% vs. 22.3%; p = 0.121) did not significantly differ between sperm donation and partner sperm AMA cycles. Male age was substantially lower (23.6 ± 5.2 vs. 41.4 ± 5.0; p < 0.0001) and oocyte yield was higher (5.1 ± 3.1 vs. 4.3 ± 2.6; p < 0.0001) in sperm donation compared to partner sperm AMA cycles, while maternal age did not vary (39.8 ± 1.6 vs. 39.6 ± 1.7; p = 0.348).

Limitations, reasons for caution

This study is limited by its retrospective nature and by differences in patients’ profiles between sperm donation and homologous cycles, although this variation has been controlled for in the statistical analysis.

Wider implications of the findings: The findings suggest that donor sperm can improve live birth rates by drastically reducing miscarriage occurrence in AMA patients. Therefore, the present results may influence AMA treatment decisions and, above all, contribute for AMA patients to achieve a healthy birth.

Trial registration number

Not applicable

P–668 We aim for one baby, not one embryo: a personalized ET strategy based on embryo score and woman age maximizes LB and minimizes twins

Study question

Is it possible to define a personalized ET model to maximize the chance of live birth (LB) while minimizing the risk of twin pregnancy?

Summary answer

A model including age and embryo morphological score can inform a personalized ET strategy to maximize LB while minimizing the risk of twin pregnancy.

What is known already

The morphological score of the transferred embryos affects pregnancy (PR) and LB rates in IVF cycles. Although SET is mainly recommended to avoid multiple pregnancies, DET is still being performed extensively, especially in patients with poor prognosis, with the aim to improve PR per transfer and shorten time to pregnancy. While twin pregnancies are associated with an increased risk of maternal and fetal complications, very low PR may increase patient drop-off, extend time to pregnancy, and increase the cost per successful transfer. A personalized transfer strategy balancing high LB per transfer with low twin pregnancy rates should be defined.

Study design, size, duration

Retrospective study including 2,470 fresh and frozen embryo transfers (ET) of either one or two embryos at D3 from January 2016 to August 2019 in a single IVF clinic. Biochemical, clinical, multiple pregnancy and live birth rates after SET and DET were analyzed according to the morphological score of the embryos transferred. ETs were divided into 9 groups according to the combinations of their embryo morphological scores.

Participants/materials, setting, methods

Embryos were assessed on D3 following a national recommended morphological scale. Morphology was categorized as High (H) if A or B+, medium (M) if B or C+, and Low (L) if C or D. The likelihood of biochemical, clinical pregnancy and live birth, and the risk of multiple pregnancy, after SET and DET of embryos of different scores was analyzed. A logistic regression analysis adjusted by age of the woman was ran for each outcome.

Main results and the role of chance

The distribution of ETs among the 9 groups for SET was: 510 H, 715 M, 346 L; for DET: 142 HH, 148 HM, 29 HL, 268 MM, 164 ML, 148 LL. Mean woman age was similar among groups: 38.7±4.01. Live birth and twin rates increased with embryo score. Considering a SET of category M as reference, the OR of live birth in DET were: 2.76 [1.82, 4.19 95%CI] for HH, and 2.32 [1.51, 3.55 95%CI] for HM, and 1.69 [1.19, 2.40 95%CI] for MM, and in SET: 1.52 [1.12, 2.04 95%CI] for H. Considering a DET of category MM as reference, the OR of twin birth in DET were: 2.8 [1.14, 6.99 95%CI] for HH, 2.5 [0.98, 6.46 95%CI] for HM, and 0.92 [0.11, 7.84 95%CI] for HL. According to this model, a 38y.o. woman with a SET of category M would have a 16% chance of live birth, and no twins. The addition of an M (DET: MM) increases her chance of live birth to 24% with a 2.9% risk of twins. The addition of a H (DET:MH) would increase further her chance of live birth to 30.8%, however, the increase would be due almost exclusively to twins (7%).

Limitations, reasons for caution

The limitations of this study are its retrospective nature and the small size of some categories. Embryos were classified using a national morphological scale; other morphological classifications could influence the results. The development and validation of site-specific models, using local patients’ data, is recommended before their use in clinical practice.

Wider implications of the findings: A personalized assessment of embryo quality and woman age, at a minimum, are necessary to identify the best ET strategy for each patient; this strategy allows to maximize live birth rates while keeping the risk of twin birth as low as possibl.

Trial registration number

Not applicable

P–637 Development and validation of an Artificial Intelligence algorithm that matches a clinician ability to select the best follitropin dose for ovarian stimulation

Study question

Is it possible for an Artificial Intelligence (AI) model to match the performance of clinicians in prescribing the first dose of follitropin?

Summary answer

The AI based Decision Support System (DSS) we developed identifies accurately the optimal starting dose range of follitropin and prospectively matches the clinicians’ performance.

What is known already

Most patients treated by IVF undergo Controlled Ovarian Stimulation (COS). Based on their ovarian markers, demographic characteristics, and clinical history, an initial dose of follitropin is prescribed. Failing to tailor correctly this dose can result in a suboptimal ovarian response, leading on the one hand to low and ineffective response or, on the other, to excessive and dangerous stimulation. AI methods can learn from large databases of COS results and generate predictive models to assist the clinicians in optimizing this decision.

Study design, size, duration

A database of 2713 first IVF cycles from 5 clinics, from 2011 to 2019 was used to develop the model. Predictor variables included: age, BMI, AMH, FSH, LH, estradiol, Antral Follicular Count (AFC), infertility etiology, and previous live births. 80% of the database was used to train the algorithm, and 20% to test the DSS. Additional 524 cycles from a different period (2020–2021) were used for prospective validation.

Participants/materials, setting, methods

Follitropin dosage was divided in 4 categories: 100–150IU, 151–200IU, 201–250IU, and >250IU. An optimal ovarian response is defined as retrieving 10–15 MII, whenever the patient ovarian reserve allows it. To predict the optimal dose range personalized to each patient, the DSS uses a Random Forest model learned with training cycles. To evaluate the DSS performance, a score for each dose range and each patient was defined given the prescribed doses and the corresponding ovarian responses.

Main results and the role of chance

The cycles included in the database were from women 37.2±4.9 years old [18–45], with a BMI of 23.7±4.2, AMH of 2.4±2.3, AFC of 11.8±7.7; the average number of oocytes and MII obtained was 10.1±7.1 and 7.2±5.3, respectively. The DSS achieved a performance mean score of 0.88 in the testing database, a value significantly better than the one calculated for the doses prescribed by the clinicians, which had a mean score of 0.83 (p-value <0.05). In the validation database the mean performance score of the DSS recommendations was 0.87, and there were no significant differences with the score of the doses actually prescribed by clinicians, also with a score of 0.86. With these results the model was shown to at least match the performance of the human doctor. It is worthy of note that the performance score value for the doses prescribed by clinicians in the validation database is relevantly higher than in the test database, closing the gap previously existing with the DSS performance. As the validation cycles are separated temporally from the rest of the cases and correspond to the newer ones, it is plausible to infer that a more experienced clinical staff would perform better.

Limitations, reasons for caution

The DSS prospective validation should be extended to more clinical cases to ensure higher reliability. Hyper-responders were underrepresented in the database which can lead to less accurate recommendation in some of these women. As all AI models, the DSS should be tested prospectively before clinical application.

Wider implications of the findings: The AI based clinical Decision Support System that we developed could be deployed as a training and learning tool for new clinicians and serve as quality control for experienced ones; further, it can be used as an electronic second opinion, for instance by providing information in peer-to-peer case discussions.

Trial registration number

Not applicable

P–159 Slow-growing embryos should be frozen on day 5

Study question

What is the live birth rate after frozen embryo transfer (FET) of slow-growing embryos frozen on day 5 (D5) or on day 6 (D6)?

Summary answer

The live birth rate after single FET is significantly higher for slow-growing embryos frozen on D5 compared to those frozen on D6.

What is known already

Most data on the outcomes of blastocyst transfer stem from studies that evaluate fresh transfer from normal growing D5 blastocyst ET. However not all embryos will begin blastulation nor reach the fully expanded stage by D5; those are the slow-growing embryos. Studies that compare D5 to D6 embryos in FET cycles show contradictory results. Some have reported higher clinical pregnancy rates after D5 FET, while others have reported similar outcomes for D5 and D6 cryopreserved blastocyst transfers. There is a lack of evidence regarding the best approach for vitrifying embryos that exhibit a slow developmental kinetic.

Study design, size, duration

This retrospective cohort study included 821 single FET of slow-growing embryos frozen on D5 or D6, belonging to patients undergoing in vitro fertilization with donor oocytes between January 2011 and October 2019, in a single fertility center. The origin of blastocysts was either supernumerary embryos after fresh embryo transfer or blastocysts from freeze-all cycles. All embryos were transferred 2- 4h after thawing.

Participants/materials, setting, methods

We compared reproductive outcomes of slow-growing embryos frozen on D5 versus (n = 442) slow-growing embryos frozen on D6 (n = 379). D5 group consisted in embryos graded 0, 1, 2 of Gardner scale and frozen on D5. Similarly, D6 group consisted in embryos graded 3, 4, 5 of Gardner scale (blastocyst stage) and frozen on D6. Differences in pregnancy rates between study groups were compared using a Chi2 test. A p-value <0.05 was considered statistically significant.

Main results and the role of chance

Baseline characteristics were comparable between study groups. Overall, mean age of the woman was 42.3±5.4 years old; donor sperm was used in 25% of cycles, and it was frozen in 73.2% of cycles. Pregnancy rates were significantly higher when transferring slow D5 embryos compared to D6 for all the pregnancy outcomes analyzed: biochemical pregnancy rate was 27.7% vs 20.2%, p < 0.016; clinical pregnancy rate was 17.5% vs 10.2%, p < 0.004); ongoing pregnancy rate was: 15.7% vs 7.8% (p < 0.001); live birth rate was: 15.4% vs 7.5%, (p < 0.001). These results suggest that when embryos exhibit a slow development behavior (not reaching full blastocysts at D5), waiting until D6 for blastulation and expansion does not improve clinical outcomes. Vitrification at D5 will should the preferred option in cases where the oocyte is assumed of high quality

Limitations, reasons for caution

The retrospective design of the study is its main limitation. Also, morphology as sole selection criterion for transfer. However, blastocyst morphology is a very good predictor of implantation and pregnancy, and a good indicator of the embryo’s chromosomal status (higher euploidy rate in higher morphological quality blastocysts).

Wider implications of the findings: These results can help to the standardization of laboratory protocols. As the decision of vitrifying slow developing embryos on D5 or D6 is made by the laboratory team or by the gynaecologist in agreement with the patient, having an evidence based strategy simplifies patient counselling and decision making.

Trial registration number

Not applicable

P–137 Male embryos take longer to develop to the blastocysts stage

Study question

Are there any differences in developmental timings between male and female preimplantation embryos?

Summary answer

There is a tendency for statistical difference in the time to reach blastocyst stage for male embryos compared to female embryos

What is known already

Differences in gene expression and metabolic uptake between male and female preimplantation embryos have been found in animal models and humans. These differences could affect the developmental timings of embryos resulting in differences in either sex. Morphokinetic parameters can precisely assess developmental timings. Only a few studies have analyzed morphokinetic parameters between male and female preimplantation embryos and no consensus has been reached on whether there is any sex-specific difference. The objective of this study is to compare morphokinetic parameters between male and female preimplantation embryos to determine any sex-specific developmental differences.

Study design, size, duration

This is a retrospective study including 102 preimplantation embryos from February 2018 to February 2020. The morphokinetic parameters obtained from time-lapse records of each embryo were: time to pronuclear fading (tPNf), times to 2–8 cells (t2, t3, t4, t5, t6, t7, t8), time to start of blastulation (tSB) and time to full blastocyst stage (tB). A two-tailed Student’s t-test was used to compare morphokinetic parameters between embryo sexes. A p < 0.05 was considered statistically significant.

Participants/materials, setting, methods

The study included retrospective time-lapse data from preimplantation embryos giving rise to 51 baby boys and 51 baby girls, as seen at birth. This is a single-center study with standardized culture conditions. Embryos in both study groups issued from cycles with donated oocytes. Only elective blastocyst stage single-embryo transfers (SET) on day 5 were assessed.

Main results and the role of chance

A tendency to statistical difference (p = [0.1–0.05]) was observed for blastocyst-related morphokinetic parameters: tSB (mean time was 89.6±6.3 hours in male embryos vs. 86.9±8.1 hours in female embryos, p = 0.06) and tB (100.2±5.9 hours versus 97.9±6.5 hours, p = 0.07). Male embryos showed an increased average time of 2.7 hours to tSB and 2.3 hours to tB, while no differences were found in the mean times of all the other morphokinetic paraments measured (p > 0.50): tPNf (∼21.8±3.0 hours) t2 (∼24.4±3.2 hours); t3 (∼35.6±3.9 hours); t4 (∼36.6±4.6 hours); t5 (∼46.9±6.0 hours); t6 (∼53.5±7.0 hours); t7 (∼54.1±7.3 hours) and t8 (∼54.1±7.3 hours). This finding suggests a sex-specific difference in reaching blastocyst stages.

Limitations, reasons for caution

The main limitation of the study is its retrospective nature and the small sample size. We analyzed the data of embryos leading to a live birth (high-quality embryos), therefore, caution should be made when generalizing results to non-implanting embryos (of potentially lower quality).

Wider implications of the findings: Sex-specific differences in developmental timings of preimplantation embryos at blastocyst stage, as evidenced by time-lapse data, should be considered to avoid selection biases during embryo transfers in ART clinic.

Trial registration number

Not applicable

Embryo biosensing by uterine natural killer cells determines endometrial fate decisions at implantation

Decidualizing endometrial stromal cells (EnSC) critically determine the maternal response to an implanting conceptus, triggering either menstruation-like disposal of low-fitness embryos or creating an environment that promotes further development. However, the mechanism that couples maternal recognition of low-quality embryos to tissue breakdown remains poorly understood. Recently, we demonstrated that successful transition of the cycling endometrium to a pregnancy state requires selective elimination of pro-inflammatory senescent decidual cells by activated uterine natural killer (uNK) cells. Here we report that uNK cells express CD44, the canonical hyaluronan (HA) receptor, and demonstrate that high molecular weight HA (HMWHA) inhibits uNK cell-mediated killing of senescent decidual cells. In contrast, low molecular weight HA (LMWHA) did not attenuate uNK cell activity in co-culture experiments. Killing of senescent decidual cells by uNK cells was also inhibited upon exposure to medium conditioned by IVF embryos that failed to implant, but not successful embryos. Embryo-mediated inhibition of uNK cell activity was reversed by recombinant hyaluronidase 2 (HYAL2), which hydrolyses HMWHA. We further report a correlation between the levels of HYAL2 secretion by human blastocysts, morphological scores, and implantation potential. Taken together, the data suggest a pivotal role for uNK cells in embryo biosensing and endometrial fate decisions at implantation.

Reproductive Outcomes in Lesbian Couples Undergoing Reception of Oocytes from Partner Versus Autologous In Vitro Fertilization/Intracytoplasmic Sperm Injection

Purpose: This study aimed to compare reproductive outcomes after Reception of Oocytes from Partner (ROPA; also called reciprocal in vitro fertilization) with those after in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) with autologous oocytes, in lesbian couples. Methods: This was a retrospective matched cohort study of couples performing a first cycle of either ROPA (n = 60) or autologous IVF/ICSI (n = 120) between February 2012 and May 2018. Couples were matched 1:2 by age of the oocyte provider, day of embryo transfer (ET), and number of embryos transferred. Pregnancy and live birth rates after the first ET and cumulative results after all subsequent ETs performed until June 2019 were evaluated. Results: Reproductive outcomes were significantly better after ROPA at first ET: biochemical pregnancy 70.0% versus 47.5% (p = 0.004), clinical pregnancy 60.0% versus 40.0% (p = 0.011), ongoing pregnancy 60.0% versus 36.7% (p = 0.003), and live birth 57.1% versus 29.8% (p = 0.001). After adjusting for age, body mass index, and number of mature oocytes, we still observed a significant improvement across all outcomes in ROPA (live birth rate odds ratio [OR]: 3.05, 95% confidence interval [CI] 1.42-6.57). Cumulative pregnancy and live birth rates were also higher after ROPA (live birth 66.1% vs. 43.4% [p = 0.005]). The adjusted analysis result for cumulative live birth was OR: 2.51, 95% CI: 1.14-5.54. Conclusion: When medically indicated, ROPA can potentially improve reproductive outcomes for lesbian couples through the possibility of selecting the best combination between two oocyte providers and two gestational mothers, provided that both women wish to participate in the pregnancy plan.

Single human oocyte transcriptome analysis reveals distinct maturation stage-dependent pathways impacted by age

Female fertility is inversely correlated with maternal age due to a depletion of the oocyte pool and a reduction in oocyte developmental competence. Few studies have addressed the effect of maternal age on the human mature oocyte (MII) transcriptome, which is established during oocyte growth and maturation, however, the pathways involved remain unclear. Here, we characterize and compare the transcriptomes of a large cohort of fully grown germinal vesicle stage (GV) and in vitro matured (IVM‐MII) oocytes from women of varying reproductive age. First, we identified two clusters of cells reflecting the oocyte maturation stage (GV and IVM‐MII) with 4445 and 324 putative marker genes, respectively. Furthermore, we identified genes for which transcript representation either progressively increased or decreased with age. Our results indicate that the transcriptome is more affected by age in IVM‐MII oocytes (1219 genes) than in GV oocytes (596 genes). In particular, we found that transcripts of genes involved in chromosome segregation and RNA splicing significantly increased representation with age, while genes related to mitochondrial activity showed a lower representation. Gene regulatory network analysis facilitated the identification of potential upstream master regulators of the genes involved in those biological functions. Our analysis suggests that advanced maternal age does not globally affect the oocyte transcriptome at GV or IVM‐MII stages. Nonetheless, hundreds of genes displayed altered transcript representation, particularly in IVM‐MII oocytes, which might contribute to the age‐related quality decline in human oocytes.

Efficiency and efficacy of vitrification in 35 654 sibling oocytes from donation cycles

STUDY QUESTION

Is oocyte vitrification/warming as efficient and effective as using fresh oocytes in donation cycles?

SUMMARY ANSWER

IVF with vitrified donor oocytes is less efficient than using fresh oocytes, but its efficacy remains comparable to that of fresh cycles.

WHAT IS KNOWN ALREADY

Oocyte vitrification is used to preserve the reproductive potential of oocytes. A small number of randomized controlled trials carried out by experienced groups have shown that this technique provides fertilization, pregnancy, implantation and ongoing pregnancy rates comparable to those of fresh oocytes. However, large registry-based analyses have consistently reported lower live birth rates (LBRs) in cycles using vitrified oocytes. It is not clear whether this decrease may be due to the effect of vitrification per se on the oocytes or to the lower efficiency of the technique, as some of the oocytes do not survive after warming.

STUDY DESIGN, SIZE, DURATION

Retrospective cohort analysis of 1844 cycles of oocyte donation (37 520 oocytes), each donor in the study provided enough oocytes for at least one reception cycle with fresh oocytes (2561 cycles) and one reception cycle with vitrified oocytes (2471 cycles) from the same ovarian stimulation (sibling oocytes). Overall, 35 654 oocytes were considered in the analysis. All embryo transfers (n = 5032) were carried out between 2011 and 2017.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Differences in reproductive outcomes after the first embryo transfer were evaluated using Pearson's Chi-squared test and regression analysis adjusted for recipient's age, BMI, sperm origin and state, day of embryo transfer, morphological score and number of transferred embryos. We performed two additional sub-analyses, to test whether the efficiency and/or effectiveness of vitrification/warming impacts reproductive results. One analysis included paired cycles where the same number of fresh and vitrified oocytes were available for ICSI (SAME sub-analysis), while the second analysis included those cycles with a 100% survival rate post-warming (SAME100 sub-analysis).

MAIN RESULTS AND THE ROLE OF CHANCE

Baseline and cycle characteristics of participants were comparable between groups. Overall, fertilization rates and embryo morphological scores were significantly lower (P < 0.001) when using vitrified oocytes; moreover, vitrified oocytes also resulted in lower reproductive outcomes than sibling fresh oocytes using both unadjusted and adjusted analyses: ongoing pregnancy (32.1% versus 37.5%; P < 0.001; OR 0.88, 95% CI 0.77, 1.00) and live birth (32.1% versus 31.9%; P = 0.92; OR 1.16, 95% CI 0.90, 1.49). However, when the efficiency of warming was taken into account, reproductive outcomes in recipients became comparable: ongoing pregnancy (33.5% versus 34.1%; P = 0.82; OR 1.11, 95% CI 0.87, 1.43) and LBR (32.1% versus 32%; P = 0.97; OR 1.15, 95% CI 0.89, 1.48). Moreover, after selecting only cycles that, in addition to having the same number of oocytes available for ICSI, also had 100% post-warming survival rate in the vitrified group, reproductive outcomes were also comparable between fresh and vitrified oocytes: ongoing pregnancy (34.8% versus 32.4%; P = 0.42; OR 1.32, 95% CI 0.98, 1.77) and live birth (32.9% versus 31.0%; P = 0.52; OR 1.27, 95% CI 0.95, 1.71), indicating that reproductive outcomes of these cycles are affected by the efficiency of the vitrification/warming technique performed rather than the oocyte damage due to the fast cooling process to which oocytes are subjected.

LIMITATIONS, REASONS FOR CAUTION

An open vitrification system was used for all cases, and oocyte vitrification/warming was performed by experienced embryologists with consistently high survival rates; caution must be exerted when extrapolating our results to data obtained using other open vitrification systems, closed vitrification systems or to IVF units with survival rates <90%.

WIDER IMPLICATIONS OF THE FINDINGS

This is the largest cohort study comparing reproductive outcomes of vitrified and fresh sibling donor oocytes to date. We found that, when the number of oocytes available after warming is equal to the number of fresh oocytes, reproductive results including live birth are comparable. Consequently, the efficiency of vitrification must be taken into account to achieve the same reproductive outcomes as with fresh oocytes. We recommend implementing strict indicators of vitrification/warming efficiency in clinics and refining vitrification/warming protocols to maximize survival.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by intramural funding of Clínica EUGIN and by the Secretary for Universities and Research of the Ministry of Economy and Knowledge of the Government of Catalonia (GENCAT 2015 DI 048). The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Altered mitochondrial function in spermatozoa from patients with repetitive fertilization failure after ICSI revealed by proteomics

BACKGROUND

Unexplained fertilization failure (FF), occurring in 1-3% of intracytoplasmic sperm injection (ICSI) cycles, results in both psychological and financial burden for the patients. However, the molecular causes behind FF remain largely unknown. Mass spectrometry is a powerful technique to identify and quantify proteins across samples; however, no study so far has used it to dissect the proteomic signature of spermatozoa with FF after ICSI.

OBJECTIVE

To investigate whether sperm samples from patients suffering repetitive FF after ICSI display alterations in their protein content.

MATERIAL AND METHODS

Seventeen infertile men were included: 5 patients presented FF in ≥3 consecutive ICSI cycles, while 12 patients had a fertilization rate >75% (controls). Individual sperm samples were subjected to 2D-LC-MS/MS. Both conventional and novel statistical approaches were used to identify differentially abundant proteins. Additionally, analysis of mitochondrial and proteasomal abundance and activity were performed, using Western blot, FACS analysis of JC-1 staining and AMC-peptide fluorometric assay.

RESULTS

Four proteins presented lower abundance (FMR1NB, FAM209B, RAB2B, and PSMA1) in the FF group compared to controls, while five mitochondrial proteins presented higher abundance in FF (DLAT, ATP5H, SLC25A3, SLC25A6, and FH) (p < 0.05). The altered abundance of mitochondrial DLAT and proteasomal PSMA1 was corroborated by Western blot. Of relevance, novel stable-protein pair analysis identified 73 correlations comprising 28 proteins within controls, while different mitochondrial proteins (ie, PDHA2, PHB2, and ATP5F1D) lost >50% of these correlations in specific FF samples pointing out specific mitochondrial deregulations.

DISCUSSION

This is the first proteomic analysis of spermatozoa from patients who resulted in fertilization failure after ICSI. The altered proteins, most of them related to mitochondrial function, could help to identify diagnostic/prognostic markers of fertilization failure and could further dissect the molecular paternal contribution to reach successful fertilization.

CONCLUSION

Sperm samples from patients with FF after ICSI present altered abundance of different proteins, including mainly mitochondrial proteins.

The ethics of preconception expanded carrier screening in patients seeking assisted reproduction

Expanded carrier screening (ECS) entails a screening offer for carrier status for multiple recessive disorders simultaneously and allows testing of couples or individuals regardless of ancestry or geographic origin. Although universal ECS—referring to a screening offer for the general population—has generated considerable ethical debate, little attention has been given to the ethics of preconception ECS for patients applying for assisted reproduction using their own gametes. There are several reasons why it is time for a systematic reflection on this practice. Firstly, various European fertility clinics already offer preconception ECS on a routine basis, and others are considering such a screening offer. Professionals involved in assisted reproduction have indicated a need for ethical guidance for ECS. Secondly, it is expected that patients seeking assisted reproduction will be particularly interested in preconception ECS, as they are already undertaking the physical, emotional and economic burdens of such reproduction. Thirdly, an offer of preconception ECS to patients seeking assisted reproduction raises particular ethical questions that do not arise in the context of universal ECS: the professional’s involvement in the conception implies that both parental and professional responsibilities should be taken into account. This paper reflects on and provides ethical guidance for a responsible implementation of preconception ECS to patients seeking assisted reproduction using their own gametes by assessing the proportionality of such a screening offer: do the possible benefits clearly outweigh the possible harms and disadvantages? If so, for what kinds of disorders and under what conditions?

Shared aspects of mRNA expression associated with oocyte maturation failure in humans and rhesus monkeys indicating compromised oocyte quality

Oocyte maturation failure observed in assisted reproduction technology (ART) cycles can limit the number of quality oocytes obtained and present a pronounced barrier for some patients. The potential exists to use unmatured oocytes for ART through in vitro maturation. Understanding the molecular basis of oocyte maturation failure is pertinent to minimizing this loss of oocytes and considerations of whether such oocytes can be used safely for ART. We identified shared transcriptome abnormalities for rhesus monkey and human failed-to-mature (FTM) oocytes relative to healthy matured MII stage oocytes. We discovered that, although the number of shared affected genes was comparatively small, FTM oocytes in both species shared effects for several pathways and functions, including predicted activation of oxidative phosphorylation (OxPhos) with additional effects on mitochondrial function, lipid metabolism, transcription, nucleotide excision repair, endoplasmic reticulum stress, unfolded protein response, and cell viability. RICTOR emerged as a prominent upstream regulator with predicted inhibition across all analyses. Alterations in KDM5A, MTOR, MTORC1, INSR, CAB39L, and STK11 activities were implicated along with RICTOR in modulating mitochondrial activity and OxPhos. Defects in cell cycle progression were not a prominent feature of FTM oocytes. These results identify a common set of transcriptome abnormalities associated with oocyte maturation failure. While our results do not demonstrate causality, they indicate that fundamental aspects of cellular function are abnormal in FTM oocytes and raise significant concerns about the potential risks of using FTM oocytes for ART.

Undetectable viral RNA in oocytes from SARS-CoV-2 positive women

A central concern for the safe provision of ART during the current coronavirus disease 2019 (CODIV-19) pandemic is the possibility of vertical transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection through gametes and preimplantation embryos. Unfortunately, data on SARS-CoV-2 viral presence in oocytes of infected individuals are not available to date. We describe the case of two women who underwent controlled ovarian stimulation and tested positive to SARS-CoV-2 infection by PCR on the day of oocyte collection. The viral RNA for gene N was undetectable in all the oocytes analyzed from the two women.

A freeze-all strategy does not increase live birth rates in women of advanced reproductive age

RESEARCH QUESTION

Does a freeze-all strategy improve live birth rates in women of different age groups?

DESIGN

Retrospective cohort study of 1882 first embryo transfer cycles, performed between January 2013 and December 2015. Reproductive outcomes between fresh (FRESH) or frozen (FROZEN) embryo transfers were compared in patients stratified by age: < 35, between 35 and 38, or > 38 years. Student's t test for independent samples and χ² analyses were used as needed. A multivariable logistic regression analysis was performed adjusting for age, triggering drug, number of retrieved oocytes, number of transferred embryos, and percentage of top-quality embryos.

MAIN RESULTS AND THE ROLE OF CHANCE

Live birth rates (LBR) were significantly higher for FROZEN in the < 35 years group (43.7% vs 24%; p < 0.001). In both the 35-38 and > 38 years groups, LBR for FROZEN vs FRESH were not statistically different (30.9% in the FROZEN group vs 29.3% in the FRESH group, p = 0.70, and 19.8% in the FROZEN group vs 12.7% in the FRESH group, p = 0.07, respectively). The multivariate analysis found a significantly positive effect of performing FROZEN on LBR in the younger group (OR 2.46, 95% CI 1.31-4.62; p = 0.005) but had no impact in women between 35 and 38 years (OR 1.01, 95% CI 0.55-1.83; p = 0.98) or older (OR 0.96, 95% CI 0.43-2.13; p = 0.92).

CONCLUSIONS

Performing a freeze-all strategy seems to result in better reproductive outcomes when compared with a fresh ET in women under 35 years, with no significant impact on older women.

Trophoblast attachment to the endometrial epithelium elicits compartment-specific transcriptional waves in an in-vitro model

RESEARCH QUESTION

Which are the early compartment-specific transcriptional responses of the trophoblast and the endometrial epithelium throughout early attachment during implantation?

DESIGN

An endometrial epithelium proxy (cell line Ishikawa) was co-cultured with spheroids of a green fluorescent protein (GFP) expressing trophoblast cell line (JEG-3). After 0, 8 and 24 h of co-culture, the compartments were sorted by fluorescence-activated cell sorting; GFP+ (trophoblast), GFP- (epithelium) and non-co-cultured control populations were analysed (in triplicate) by RNA-seq and gene set enrichment analysis (GSEA).

RESULTS

Trophoblast challenge induced a wave of transcriptional changes in the epithelium that resulted in 295 differentially regulated genes involving epithelial to mesenchymal transition (EMT), cell movement, apoptosis, hypoxia, inflammation, allograft rejection, myogenesis and cell signalling at 8 h. Interestingly, many of the enriched pathways were subsequently de-enriched by 24 h (i.e. EMT, cell movement, allograft rejection, myogenesis and cell signalling). In the trophoblast, the co-culture induced more transcriptional changes and regulation of a variety of pathways. A total of 1247 and 481 genes were differentially expressed after 8 h and from 8 to 24 h, respectively. Angiogenesis and hypoxia were over-represented at both stages, while EMT and cell signalling only were at 8 h; from 8 to 24 h, inflammation and oestrogen response were enriched, while proliferation was under-represented.

CONCLUSIONS

Successful attachment produced a series of dynamic changes in gene expression, characterized by an overall early and transient transcriptional up-regulation in the receptive epithelium, in contrast to a more dynamic transcriptional response in the trophoblast.

Novel phospholipase C zeta 1 mutations associated with fertilization failures after ICSI

STUDY QUESTION

Are phospholipase C zeta 1 (PLCZ1) mutations associated with fertilization failure (FF) after ICSI?

SUMMARY ANSWER

New mutations in the PLCZ1 sequence are associated with FFs after ICSI.

WHAT IS KNOWN ALREADY

FF occurs in 1-3% of ICSI cycles, mainly due to oocyte activation failure (OAF). The sperm PLCζ/PLCZ1 protein hydrolyzes phosphatidylinositol (4, 5)-bisphosphate in the oocyte, leading to intracellular calcium release and oocyte activation. To date, few PLCZ1 point mutations causing decreased protein levels or activity have been linked to FF. However, functional alterations of PLCζ/PLCZ1 in response to both described and novel mutations have not been investigated.

STUDY DESIGN, SIZE, DURATION

We performed a study including 37 patients presenting total or partial FF (fertilization rate (FR), ≤25%) after ICSI occurring between 2014 and 2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients were divided into two groups based on oocyte evaluation 19 h post ICSI: FF due to a defect in oocyte activation (OAF, n = 22) and FF due to other causes ('no-OAF', n = 15). Samples from 13 men with good fertilization (FR, >50%) were used as controls. PLCζ/PLCZ1 protein localization and levels in sperm were evaluated by immunofluorescence and western blot, respectively. Sanger sequencing on genomic DNA was used to identify PLCZ1 mutations in exonic regions. The effect of the mutations on protein functionality was predicted in silico using the MODICT algorithm. Functional assays were performed by cRNA injection of wild-type and mutated forms of PLCZ1 into human in vitro matured metaphase II oocytes, and fertilization outcomes (second polar body extrusion, pronucleus appearance) scored 19 h after injection.

MAIN RESULTS AND THE ROLE OF CHANCE

In the OAF group, 12 (54.6%) patients carried at least one mutation in the PLCZ1 coding sequence, one patient out of 15 (6.7%) in the no-OAF group (P < 0.05) and none of the 13 controls (P < 0.05). A total of six different mutations were identified. Five of them were single-nucleotide missense mutations: p.I120M, located at the end of the EF-hand domain; p.R197H, p.L224P and p.H233L, located at the X catalytic domain; and p.S500 L, located at the C2 domain. The sixth mutation, a frameshift variant (p.V326K fs*25), generates a truncated protein at the X-Y linker region. In silico analysis with MODICT predicted all the mutations except p.I120M to be potentially deleterious for PLCζ/PLCZ1 activity. After PLCZ1 cRNA injection, a significant decrease in the percentage of activated oocytes was observed for three mutations (p.R197H, p.H233L and p.V326K fs*25), indicating a deleterious effect on enzymatic activity. PLCZ1 protein localization and expression levels in sperm were similar across groups. FRs were restored (to >60%) in patients carrying PLCZ1 mutations (n = 10) after assisted oocyte activation (AOA), with seven patients achieving pregnancy and live birth.

LIMITATIONS, REASONS FOR CAUTION

Caution should be exerted when comparing the cRNA injection results with fertilization outcomes after ICSI, especially in patients presenting mutations in heterozygosis.

WIDER IMPLICATIONS OF THE FINDINGS

PLCZ1 mutations were found in high frequency in patients presenting OAF. Functional analysis of three mutations in human oocytes confirms alteration of PLCζ/PLCZ1 activity and their likely involvement in impaired oocyte activation. Our results suggest that PLCZ1 gene sequencing could be useful as a tool for the diagnosis and counseling of couples presenting FF after ICSI due to OAF.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by intramural funding of Clínica EUGIN, by the Secretary for Universities and Research of the Ministry of Economy and Knowledge of the Government of Catalonia (GENCAT 2015 DI 049 to M. T.-M. and GENCAT 2015 DI 048 to D. C.-B.) and by the Torres Quevedo Program from the Spanish Ministry of Economy and Competitiveness to A. F.-V. No competing interest declared.

Comparison of two different oocyte vitrification methods: a prospective, paired study on the same genetic background and stimulation protocol

STUDY QUESTION

Can two different methods for oocyte vitrification, one using an open tool and the other a closed tool, result in similar oocyte survival rates?

SUMMARY ANSWER

The oocyte survival rate was found to be higher in the closed method.

WHAT IS KNOWN ALREADY

Open vitrification is performed routinely in oocyte donation cycles. Closed oocyte vitrification may result in slower cooling rates and thus it is less used, even though it has been recommended in order to avoid the risk of cross-contamination between material from different patients.

STUDY DESIGN, SIZE, DURATION

This is a prospective cohort study with sibling oocytes carried out in a fertility center between July 2014 and January 2016. The study included 83 oocyte donors each providing a minimum of 12 mature oocytes (metaphase II: MII) at oocyte retrieval. Oocyte survival rate and fertilization rate, as well as reproductive outcomes (biochemical, clinical, ongoing pregnancy and live birth rates) per embryo transfer and also cumulatively between the two methods were compared by Chi2 tests.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Donor oocytes were denuded and six MII oocytes from each donor were vitrified using an open method and later assigned to one recipient, while another six MII oocytes were vitrified using a closed method and assigned to a different recipient (paired analysis). ICSI was used in all cases and embryo transfer was performed on Day 2-3 in all cases.

MAIN RESULTS AND THE ROLE OF CHANCE

Oocyte donors were 24.8 years old on average (SD 4.7). Recipient age (average 41.2 years, SD 4.7) and BMI (mean 23.8 kg/m2, SD 4.0) were similar between recipient groups. Oocytes vitrified using the closed method had higher survival rate (94.5% versus 88.9%, P = 0.002), but lower fertilization rate (57.1% versus 69.8%, P < 0.001) compared to the open method. The number of fresh embryos transferred in the two groups was 1.8 on average (SD 0.4). Biochemical (45% closed versus 50% open), clinical (40% versus 50%) and ongoing (37.5% versus 42.5%) pregnancy rates were not different between groups (P > 0.05) and neither were live birth rates (37.5% versus 42.5%, P > 0.05). Cumulative reproductive results (obtained after the transfer of all the embryos) were also similar between groups.

LIMITATIONS, REASONS FOR CAUTION

The participants of this study were oocyte donors, i.e. young women in good health, and care should be exerted in extending our results to other populations such as infertility patients, oncofertility patients and women freezing oocytes to delay childbearing.

WIDER IMPLICATIONS OF THE FINDINGS

Our results suggest that, in spite of different survival and fertilization rates, closed and open oocyte vitrification methods should offer similar reproductive outcomes up to cumulative live birth rates.

STUDY FUNDING/COMPETING INTEREST(S)

The authors report no conflict of interest. Vitrolife provided the media and the closed method tool needed for the study at no cost.

Altered cytoplasmic maturation in rescued in vitro matured oocytes

STUDY QUESTION

Do culture conditions affect cytoplasmic maturation in denuded immature non-GV oocytes?

SUMMARY ANSWER

The maturation rate of denuded non-GV oocytes is not affected by culture media, but in vitro maturation seems to alter the mitochondrial membrane potential, endoplasmic reticulum (ER) and actin cytoskeleton compared with in vivo maturation.

WHAT IS KNOWN ALREADY

In vitro maturation of denuded immature non-GV oocytes benefits cycles with poor in vivo MII oocyte collection, but maturation levels of non-GV oocytes are only scored by polar body extrusion. Since oocyte maturation involves nuclear as well as cytoplasmic maturation for full meiotic competence, further knowledge is needed about cytoplasmic maturation in in vitro culture.

STUDY DESIGN, SIZE, DURATION

This basic research study was carried out between January 2017 and September 2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 339 denuded immature non-GV oocytes were cultured in SAGE 1-Step (177) or G-2 PLUS (162) for 6-8 h after retrieval, and 72 in vivo matured MII oocytes were used as controls. Cultured immature non-GV oocytes were scored for polar body extrusion and analysed for mitochondrial membrane potential (ΔΨm), ER clusters, cortical granules number and distribution, spindle morphology and actin cytoskeleton organization. The obtained parameter values were compared to in vivo matured MII oocyte parameter values.

MAIN RESULTS AND THE ROLE OF CHANCE

The maturation rates of oocytes cultured in G-2 PLUS and SAGE 1-Step were similar (65% vs 64.2%; P = 0.91). The differences observed in cortical granule density were not statistically significant. Also spindle morphometric parameters were mostly similar between in vitro and in vivo matured MII oocytes. However, the number of ER clusters, the ΔΨm and the cortical actin thickness showed significant differences between in vivo MII oocytes and denuded immature non-GV oocytes cultured in vitro until meiosis completion.

LIMITATIONS, REASONS FOR CAUTION

Frozen-thawed oocytes together with fresh oocytes were used as controls. Due to technical limitations (fixation method and fluorochrome overlap), only one or two parameters could be studied per oocyte. Thus, a global view of the maturation status for each individual oocyte could not be obtained.

WIDER IMPLICATIONS OF THE FINDINGS

Characterization of in vitro matured oocytes at the cellular level will help us to understand the differences observed in the clinical outcomes reported with rescue IVM compared to in vivo MII oocytes and to improve the culture methods applied.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by intramural funding of Clinica Eugin and by the Torres Quevedo Program to A.F.-V. from the Spanish Ministry of Economy and Competitiveness. No competing interests are declared.