Clinical Implications of Paternal Age in Assisted Reproduction: Integrating Sperm Epigenetic Evidence

Background: Advanced paternal age is increasingly encountered in assisted reproduction as parenthood is deferred. The clinical question is whether paternal age from about 40 to 45 years and older affects embryo development or outcomes, and to what extent any effect relates to the sperm epigenome. Methods: This narrative review synthesized PubMed-indexed evidence on sperm aging biology, including DNA methylation, chromatin packaging and nucleosome retention, small non-coding RNAs, telomere dynamics, DNA fragmentation, and oxidative and mitochondrial stress, and their potential clinical impact on assisted reproduction outcomes. Results: Maternal age remains the principal determinant of embryo aneuploidy. After multivariable adjustment, independent paternal-age effects on fertilization, blastocyst formation, and preimplantation genetic testing for aneuploidy are small or not detected. At very advanced paternal ages near or above 50 years, some studies report higher miscarriage and lower live birth, without a consistent change in early embryo morphology. Aging in men is linked to higher DNA fragmentation and oxidative and mitochondrial signatures, together with reproducible sperm-epigenome changes, including age-linked DNA methylation, altered histone retention, and small-RNA shifts. These molecular findings support modest intergenerational influences on early development, while stable transgenerational inheritance in humans is not supported. Conclusions: Advanced paternal age should be regarded as a risk modifier rather than a primary driver of preimplantation failure. Counseling should emphasize realistic effect sizes and the predominance of maternal age. Laboratory workflows should minimize oxidative stress. Selective DNA-fragmentation testing may be appropriate in recurrent ART failure or recurrent loss. Sperm-epigenome assays remain investigational and should undergo prospective, standardized validation before use in routine care.