Schematic of experimental paradigm. Oocytes and cumulus–oocyte complexes (COCs) from reproductively young (6–12 weeks) and old (9–12 months) mice were matured in vitro (IVM) in media supplemented with human follicular fluid (FF) from mid-reproductive age participants (32–36 years) to investigate dose-dependent effects, or with FF from reproductively young (28–31 years) or old (39–42 years) to investigate age-dependent effects, on oocyte quality. Meiotic progression, spindle morphology, chromosome alignment, ploidy, mitochondrial distribution and function, as well as cumulus expansion were evaluated following IVM. This figure was created with BioRender.com.