Oocyte meiotic spindle morphology is a predictive marker of blastocyst ploidy-a prospective cohort study.

Objective: To evaluate oocyte meiotic spindle (OMS) morphology at intracytoplasmic sperm injection (ICSI) as a predictor of blastocyst ploidy and whether OMS morphology could aid standard morphology-based blastocyst selection.

Design: Prospective cohort study.

Setting: In vitro fertilization clinic.

Patient(s): Patients undergoing ICSI cycles with an intention to perform preimplantation genetic testing for aneuploidy (PGT-A) from October 2014 to December 2017.

Intervention(s): The OMS was visualized with the use of polarized light microscopy at the time of ICSI and the morphology classified as normal, dysmorphic, translucent, not visible, or in telophase. Blastocyst biopsy for PGT-A was performed on embryos with suitable development.

Main Outcome Measure(s): The association of OMS morphology with the resulting blastocyst ploidy was evaluated on an "intention-to-treat" (ITT) and an "as-treated analysis" (ATA) basis.

Result(s): The morphology of 2,056 OMSs were classified. A strong association of OMS morphology with fertilization, cleavage to at least 6 cells on day 3, and good/top-quality blastocyst formation was present. Normal OMS was positively associated with blastocyst euploidy compared with all other OMS types combined, per either ITT or ATA. Even after controlling for female age, blastocyst quality, and developmental stage, the presence of a normal OMS was strongly associated with the probability of blastocyst euploidy.

Conclusion(s): OMS morphology is a predictive marker of blastocyst ploidy and can potentially aid standard morphology-based blastocyst selection.