• Autologous BMSC mitochondrial transplantation did not improve clinical pregnancy or live birth rates in unselected patients with recurrent ART failure.
• MIT transiently accelerated early embryonic cleavage but did not enhance day-3 good-quality embryo rates.
• Long-term follow-up of 23 live births showed no adverse effects, supporting the safety of the procedure.
• A higher burden of medium-frequency mtDNA point mutations may predict favorable response to MIT, suggesting a role for molecular stratification.