Fertilization time and oocyte spindle integrity: implication for embryo ploidy

Area of Science:

• Reproductive biology
• Assisted reproductive technology
• Genetics

Background:

• Oocyte maturation is crucial for successful fertilization and embryo development.
• Assessing oocyte quality and predicting embryo ploidy are key challenges in assisted reproductive technology (ART).
• The meiotic spindle (MS) plays a vital role in chromosome segregation during oocyte maturation.

Purpose of the Study:

• To investigate if meiotic spindle (MS) visibility in human oocytes predicts nuclear maturation and embryo ploidy.
• To determine the impact of the interval between ovulation triggering and ICSI fertilization on embryo chromosomal status.
• To provide evidence for spindle-guided assessment of oocyte quality to improve prediction of embryo ploidy, particularly in women of advanced maternal age.

Main Methods:

• Retrospective study analyzing 1,879 oocytes undergoing preimplantation genetic testing for aneuploidy (PGT-A).
• Meiotic spindle (MS) visibility assessed using polarized light microscopy.
• Trigger-to-fertilization interval adjusted to optimize oocyte maturation and analyzed for its effect on embryo euploidy.

Main Results:

• Extending the trigger-fertilization interval based on MS status increased mature oocyte proportion from 79% to 92% (p < 0.05).
• Embryos from immature oocytes (no visible MS) had a 14% euploidy rate, compared to 42% from mature oocytes (visible MS) (p < 0.05).
• A trigger-ICSI interval of 40-44 hours resulted in a higher euploidy rate (47%) than 36-39 hours (33%) (p < 0.05).

Conclusions:

• Meiotic spindle (MS) visibility is a reliable predictor of oocyte nuclear maturation and subsequent embryo ploidy.
• Optimizing the timing of ICSI relative to ovulation trigger, guided by MS assessment, can enhance embryo euploidy rates.
• Spindle-guided oocyte assessment offers a valuable tool for improving ART outcomes, especially for women with advanced maternal age and increased aneuploidy risk.