Distinct post-insemination dynamics between fresh and frozen-derived gametes using testicular sperm

Area of Science:

• Reproductive Medicine
• Infertility Research
• Sperm Cryopreservation

Background:

• Testicular sperm extraction (TESE) is a method for retrieving sperm in cases of non-obstructive azoospermia (NOA).
• The use of frozen-thawed sperm and oocytes in assisted reproductive technologies (ART) is common, but its impact on early post-insemination events requires evaluation.

Purpose of the Study:

• To compare post-insemination outcomes between fresh and frozen-derived gametes when using TESE sperm.
• To investigate the effects of fresh versus frozen testicular sperm and oocytes on fertilization, blastocyst development, and euploidy rates.

Main Methods:

• A retrospective cohort study analyzed 72 cycles involving 980 oocytes from 30 couples undergoing TESE.
• Gametes included fresh or frozen-thawed TESE sperm and fresh or vitrified oocytes from the same patients.
• Embryos were cultured in a time-lapse incubator, with blastocysts undergoing trophectoderm biopsy for preimplantation genetic testing for aneuploidy (PGT-A).

Main Results:

• Frozen-TESE sperm was associated with significantly lower fertilization and blastulation rates compared to fresh TESE sperm.
• Euploidy rates per tested blastocyst were similar for fresh and frozen-TESE sperm, but not significantly affected by frozen oocyte use.
• Both frozen-TESE sperm and vitrified oocytes showed a significantly longer 2-pronuclear (2PN) to 4-cell (PNf) stage duration, indicating delayed pronuclear development.

Conclusions:

• Synchronizing fresh TESE sperm retrieval with oocyte retrieval may optimize fertilization outcomes.
• The observed delay in 2PN development with frozen gametes suggests potential post-thaw nuclear repair mechanisms that warrant further investigation.