Reconsideration of the safety and effectiveness of human oocyte cryopreservation

Dimethyl sulfoxide-induced DNA demethylation during vitrification of early cleavage-stage embryos and possible countermeasures

PURPOSE

Dimethyl sulfoxide (DMSO) alters DNA methylation in vitrified-warmed embryos and potentially affects subsequent development. This study aimed to examine possible countermeasures against DMSO-induced demethylation.

METHODS

In vitro-produced bovine embryos (8-cell stage) were vitrified using a combination of DMSO and ethylene glycol (EG) or propylene glycol (PG) + EG. After warming, the lipid content and expression levels of 5-methylcytosine (5mC), 5-hydroxymethylcytosine (5hmC), DNMTs, and TETs were examined. In addition, RNA-sequencing was performed on blastocysts derived from the vitrified embryos. Furthermore, the effect of supplementation with a vitrification medium containing DMSO and N-acetyl-L-cysteine (NAC, 5 mM) on the levels of 5mC in embryos was examined.

RESULTS

Vitrification decreased the levels of 5mC and increased the levels of 5hmC in 8-cell stage embryos. Low levels of 5mC persisted until the blastocyst stage in the DMSO group but increased in the PG group. The expression level of TET3A was higher in the DMSO group than in the fresh group, but not in the PG group. Both cryoprotectants reduced the lipid levels in post-warmed 8-cell stage embryos. The addition of NAC ameliorated DMSO-induced demethylation at both the 8-cell and blastocyst stages. RNA-seq analysis revealed that PG-specific pathways included ribosomes and mitochondria and that both DMSO and PG affected cGMP-PGK, MAPK, Wnt, and insulin secretion-related signaling. The K-medoids method predicted that DMSO affected cell adhesion molecules and that MAPK signaling was affected the most.

CONCLUSIONS

PG and NAC may antagonize DMSO-induced demethylation; however, PG exerts adverse effects on embryos.

Ultra-fast vitrification and rapid elution of human oocytes: Part II - verification of blastocyst development from mature oocytes

RESEARCH QUESTION

Will ultra-fast vitrification (UFV) and rapid elution of mature human oocytes retain the reliable, high survival rates and meiotic spindle normality seen in the germinal vesicle model, and will these oocytes maintain their developmental competence to form blastocyst-stage embryos following artificial oocyte activation (AOA)?

DESIGN

Conventional vitrification treatment was compared with UFV treatment in mature, germinal-vesicle-derived oocytes (Phase 2, Expt. 2, n = 50) and substandard donor oocytes, metaphase I-metaphase II (MII) oocytes and poor-quality MII oocytes (n = 222). Post-warming survival, the integrity of the meiotic spindle and AOA-related development were assessed.

RESULTS

Overall survival rates were higher (P = 0.003) for UFV/rapid elution treatment (94-100%, mean = 98%) compared with conventional vitrification/control dilution treatment (80-90%, mean = 83.3%). MII oocytes derived from immature germinal vesicles following conventional vitrification/control dilution or UFV/rapid elution treatments proved to be capable of activated development (54-71% cleavage rate), with four blastocysts produced. AOA treatment with DMAP exposure yielded optimal activated development. When vitrifying mature oocytes, both UFV and conventional vitrification treatments exhibited normal activated development and blastocyst production (34.9% and 31.7%, respectively).

CONCLUSIONS

Considering that oocyte freezing was deemed non-experimental based primarily on healthy live births from frozen-oocyte-derived embryo transfer the validation of normal blastocyst formation using the novel UFV approach is a critical accomplishment. The UFV method for oocyte cryopreservation represents a strategic deviation from traditional semi-equilibration vitrification protocols. UFV is a more time-efficient approach that consistently yields a higher survival rate, and thus has the potential to create more embryos. These findings justify proceeding with strategic clinical trial applications.

Is there a preferred time interval between gonadotropin-releasing hormone (GnRH) agonist trigger and oocyte retrieval in GnRH antagonist cycles? A retrospective cohort of planned fertility preservation cycles

BACKGROUND

The ideal time frame between gonadotropin-releasing hormone (GnRH) agonist (GnRHa) trigger administration and oocyte retrieval in GnRH antagonist cycles has not been well studied. Our goal was to evaluate the effect of this time interval on oocyte yield and oocyte maturation rate in GnRH antagonist cycles designated for non-medical ("planned") oocyte cryopreservation.

METHODS

We conducted a retrospective cohort study including patients who underwent elective fertility preservation, using the GnRH antagonist protocol and exclusively triggered by GnRH-agonist. We focused on the effect of the trigger-to-retrieval time interval on oocyte yield and maturation rate, while also incorporating age, body mass index (BMI), anti-Müllerian hormone (AMH) levels, basal Follicle-Stimulating Hormone (FSH) levels, as well as the type and dosage of gonadotropin FSH medication.

RESULTS

438 cycles were included. Trigger-to-retrieval time interval ranged from 32.03 to 39.92 h. The mean oocyte yield showed no statistically significant difference when comparing retrievals < 36 h (n = 240, 11.86 ± 8.6) to those triggered at ≥ 36 h (n = 198, 12.24 ± 7.73) (P = 0.6). Upon dividing the cohort into four-time quartiles, no significant differences in the number of retrieved oocytes were observed (P = 0.54). Multivariate regression analysis failed to reveal any significant associations between the interval and the aforementioned variables.

CONCLUSIONS

The GnRHa trigger to oocyte retrieval interval range in our cohort did not significantly affect oocyte yield and maturation rate.

Fatty acid supplementation during warming improves pregnancy outcomes after frozen blastocyst transfers: a propensity score-matched study

This study aimed to examine the viability of human blastocysts after warming with fatty acids (FAs) using an in vitro outgrowth model and to assess pregnancy outcomes after a single vitrified-warmed blastocyst transfer (SVBT). For the experimental study, we used 446 discarded vitrified human blastocysts donated for research purposes by consenting couples. The blastocysts were warmed using FA-supplemented (FA group) or non-FA-supplemented (control group) solutions. The outgrowth area was significantly larger in the FA group (P = 0.0428), despite comparable blastocyst adhesion rates between the groups. Furthermore, the incidence of outgrowth degeneration was significantly lower in the FA group than in the control group (P = 0.0158). For the clinical study, we retrospectively analyzed the treatment records of women who underwent SVBT in natural cycles between January and August 2022. Multiple covariates that affected the outcomes were used for propensity score matching as follows: 1342 patients in the FA group were matched to 2316 patients in the control group. Pregnancy outcomes were compared between the groups. The rates of implantation, clinical pregnancy, and ongoing pregnancy significantly increased in the FA group after SVBTs (P = 0.0091-0.0266). These results indicate that warming solutions supplemented with FAs improve blastocyst outgrowth and pregnancy outcomes after SVBTs.