Methods for Assessing Oocyte Quality: A Review of Literature

Use of assisted reproductive technologies (ARTs) to shorten the generational interval in ruminants: current status and perspectives

The challenges posed by climate change and increasing world population are stimulating renewed efforts for improving the sustainability of animal production. To meet such challenges, the contribution of genomic selection approaches, in combination with assisted reproductive technologies (ARTs), to spreading and preserving animal genetics is essential. The largest increase in genetic gain can be achieved by shortening the generation interval. This review provides an overview of the current status and progress of advanced ARTs that could be applied to reduce the generation time in both female and male of domestic ruminants. In females, the use of juvenile in vitro embryo transfer (JIVET) enables to generate offspring after the transfer of in vitro produced embryos derived from oocytes of prepubertal genetically superior donors reducing the generational interval and acceleration genetic gain. The current challenge is increasing in vitro embryo production (IVEP) from prepubertal derived oocytes which is still low and variable. The two main factors limiting IVEP success are the intrinsic quality of prepubertal oocytes and the culture systems for in vitro maturation (IVM). In males, advancements in ARTs are providing new strategies to in vitro propagate spermatogonia and differentiate them into mature sperm or even to recapitulate the whole process of spermatogenesis from embryonic stem cells. Moreover, the successful use of immature cells, such as round spermatids, for intracytoplasmic injection (ROSI) and IVEP could allow to complete the entire process in few months. However, these approaches have been successfully applied to human and mouse whereas only a few studies have been published in ruminants and results are still controversial. This is also dependent on the efficiency of ROSI that is limited by the current isolation and selection protocols of round spermatids. In conclusion, the current efforts for improving these reproductive methodologies could lead toward a significant reduction of the generational interval in livestock animals that could have a considerable impact on agriculture sustainability.

Impact of oxygen tension during in vitro maturation: a sibling-oocyte prospective double-blinded study

OBJECTIVE

To determine whether oxygen (O2) tension (20% vs. 5%) has an impact on oocyte maturation rates and morphology during in vitro maturation (IVM).

DESIGN

A prospective, observational, monocentric, sibling-oocyte study.

SETTING

University Hospital.

PATIENTS

A total of 143 patients who underwent IVM for fertility preservation purposes from November 2016 to April 2021 were analyzed. Patients were included when ≥2 cumulus-oocyte complexes (COCs) were retrieved. The cohort of COCs obtained for each patient was randomly split into two groups: group 20% O2 and group 5% O2.

INTERVENTION

Cumulus-oocyte complexes were incubated for 48 hours either under 5% O2 or 20% O2. After 24 and 48 hours of culture, every oocyte was assessed for maturity and morphology, to estimate oocyte quality. Morphology was evaluated considering six parameters (shape, size, ooplasm, perivitelline space, zona pellucida, and polar body characteristics), giving a total oocyte score ranging from -6 to +6.

MAIN OUTCOME MEASURES

Maturation rates and total oocyte scores were compared using paired-sample analysis between group 20% O2 and group 5% O2.

RESULTS

Patient median age was 31.4 [28.1-35.2] years-old. The mean serum antimüllerian hormone levels and antral follicle count were 3.2 ± 2.3 ng/mL and 27.2 ± 16.0 follicles, respectively. A mean of 10.7 COCs per cycle were retrieved, leading to 6.1 ± 2.4 metaphase II oocytes vitrified (total maturation rate = 57.3%; 991 metaphase II oocytes/1,728 COCs). A total of 864 COCs were included in each group. Oocyte maturation rates were not different between the two groups (group 20% O2: 56.82% vs. group 5% O2: 57.87%, respectively). Regarding oocyte morphology, the mean total oocyte score was significantly higher in group 5% O2 compared with group 20% O2 (3.44 ± 1.26 vs. 3.16 ± 1.32, P=.014).

CONCLUSION

As culture under low O2 tension (5% O2) improves oocyte morphology IVM, our results suggest that culture under hypoxia should be standardized. Additional studies are warranted to assess the impact of O2 tension on oocyte maturation and the benefit of IVM under low O2 tension for embryo culture after utilization of frozen material.

Effect of split weaning on follicle development and oocyte quality in multiparous sows

Increasing piglet weaning age while maintaining the reproductive efficiency of the breeding herd depends on being able to stimulate sows to ovulate during lactation without reducing subsequent pregnancy rates and litter sizes. Embryo survival is affected by the quality of the oocytes shed at ovulation, and oocyte quality is profoundly impacted by the follicular environment in which the oocyte matures. This study determined the effect of reducing suckled litter size from 11 to 7 piglets on day 18 of lactation on the ovarian follicular environment and oocyte developmental competence at day 21 of lactation. Thirty-nine, Large White X Landrace sows (parity 3.2 ± 0.2; mean ± SEM; range 2-6) had their litter size either maintained at 11 piglets (control); or reduced to seven piglets on day 18 of lactation (split wean (SW)). Sows were slaughtered on day 21 of lactation and ovaries were collected for analysis of follicular fluid composition and in vitro blastocyst development rates. There was no effect of split weaning on fertilisation rate and development to blastocyst stage; however, a greater proportion of blastocysts from control sows were classified as early blastocyst stage. Furthermore, follicular fluid concentrations of oestradiol were higher in SW sows. Together, these results indicate split weaning prior to mating in lactation alters the ovarian follicular environment and while blastocyst development rates were unaffected, embryos from control sows may be of poorer quality as indicated by a delay in development.

The prospect of artificial intelligence to personalize assisted reproductive technology

Infertility affects 1-in-6 couples, with repeated intensive cycles of assisted reproductive technology (ART) required by many to achieve a desired live birth. In ART, typically, clinicians and laboratory staff consider patient characteristics, previous treatment responses, and ongoing monitoring to determine treatment decisions. However, the reproducibility, weighting, and interpretation of these characteristics are contentious, and highly operator-dependent, resulting in considerable reliance on clinical experience. Artificial intelligence (AI) is ideally suited to handle, process, and analyze large, dynamic, temporal datasets with multiple intermediary outcomes that are generated during an ART cycle. Here, we review how AI has demonstrated potential for optimization and personalization of key steps in a reproducible manner, including: drug selection and dosing, cycle monitoring, induction of oocyte maturation, and selection of the most competent gametes and embryos, to improve the overall efficacy and safety of ART.

Disturbed Follicular Microenvironment in Polycystic Ovary Syndrome: Relationship to Oocyte Quality and Infertility

Polycystic ovary syndrome (PCOS) is a common endocrine disorder associated with infertility and poor reproductive outcomes. The follicular fluid (FF) microenvironment plays a crucial role in oocyte development. This review summarizes evidence elucidating the alterations in FF composition in PCOS. Various studies demonstrated a pronounced proinflammatory milieu in PCOS FF, characterized by increased levels of cytokines, including but not limited to interleukin-6 (IL-6), tumor necrosis factor α, C-reactive protein, and IL-1β, concomitant with a reduction in anti-inflammatory IL-10. T lymphocytes and antigen-presenting cells are dysregulated in PCOS FF. PCOS FF exhibit heightened reactive oxygen species production and the accumulation of lipid peroxidation byproducts, and impaired antioxidant defenses. Multiple microRNAs are dysregulated in PCOS FF, disrupting signaling critical to granulosa cell function. Proteomic analysis reveals changes in pathways related to immune responses, metabolic perturbations, angiogenesis, and hormone regulation. Metabolomics identify disturbances in glucose metabolism, amino acids, lipid profiles, and steroid levels with PCOS FF. Collectively, these pathological alterations may adversely affect oocyte quality, embryo development, and fertility outcomes. Further research on larger cohorts is needed to validate these findings and to forge the development of prognostic biomarkers of oocyte developmental competence within FF. Characterizing the follicular environment in PCOS is key to elucidating the mechanisms underlying subfertility in this challenging disorder.

Differential transcript usage across mammalian oocytes at the germinal vesicle and metaphase II stages

Ongoing progress in mRNA-Sequencing technologies has significantly contributed to the refinement of assisted reproductive technologies. However, the prior investigations have predominantly concentrated on alterations in overall gene expression levels, thereby leaving a considerable gap in our understanding of the influence of transcript isoform expression on fundamental cellular mechanisms of oocytes. Given the efficacy of differential transcript usage (DTU) analysis to address such knowledge, we conducted comprehensive DTU analysis utilizing mRNA-Seq datasets of germinal vesicle (GV) and metaphase II (MII) oocytes across six mammalian species from the SRA database, including cow, donkey, horse, human, mouse, and pig. To further illuminate the roles of these genes, we also conducted a rigorous Gene Ontology (GO) term enrichment analysis. While the DTU analysis of each species exhibited several genes with alterations in their transcript isoform usage, referred to as DTU genes, this study focused on only ten cross-species DTU genes sharing among a minimum of five distinct species (FDR≤0.05). These cross-species DTU genes were as follows: ABCF1, CDC6, CFAP36, CNOT10, DNM3, IWS1, NBN, NDEL1, RAD50 and ZCCHC17. GO term enrichment analysis unveiled the alignment of these cross-species DTU gene functions with RNA and cell-cycle control mechanisms across diverse mammalian species, thereby suggesting their vital roles during oocyte maturation. Further exploration of the transcript isoforms of these genes hence bore the potential to uncover novel transcript isoform markers for future reproductive technologies in both human and animal contexts.

Efficacy and safety of recombinant human granulocyte colony-stimulating factor in patients with poor ovarian response: protocol for a multicentre, randomised, controlled trial

INTRODUCTION

Approximately 17.5% of couples of reproductive age have experienced infertility. Women with a poor ovarian response (POR) must undergo in vitro fertilisation (IVF) and embryo transfer to achieve pregnancy. However, studies have reported a poor response to gonadotropin stimulation in women undergoing IVF-ET. Results from animal experiments suggest that granulocyte colony-stimulating factor (G-CSF) has a curative effect by protecting ovarian function, reducing follicle loss and delaying premature ovarian failure in rats caused by chemotherapy. Clinical studies on the therapeutic effect of G-CSF are deficient; therefore, this study will investigate its ability to improve ovum quality and maturity among women with POR undergoing IVF/intracytoplasmic sperm injection (ICSI).

METHODS AND ANALYSIS

This clinical, multicentre, triple-blind, placebo-controlled trial will employ balanced randomisation (1:1). The planned sample size is 312 participants (156 subjects in each group). A total of 312 patients with infertility undergoing IVF/ICSI will be recruited from four public hospitals in China. The participants will be randomly divided into an experimental group (G-CSF) and a placebo group (control). All patients will be treated by using the progestin-primed ovarian stimulation superovulation protocol. The primary outcome will be D3 embryo quality. The number of ova obtained, MII ova and transferable embryos will be inclusive in the secondary outcome.

ETHICS AND DISSEMINATION

To our knowledge, this is the first clinical trial to investigate the effect of G-CSF treatment timing and stimulation protocol in patients with POR in China. This study will provide new information about G-CSF efficacy among patients with POR undergoing IVF/ICSI and can help improve ovum quality and maturity. Clinical trials on this subject are deficient in China; therefore, a well-designed randomised trial is needed to determine the ability of G-CSF to improve ovum quality and maturity to facilitate conception among women with POR treated with IVF/ICSI.

TRIAL REGISTRATION NUMBER

ChiCTR2200062412.