MOLECULAR-MORPHOLOGICAL DISSOCIATION IN VITRIFIED-WARMED HUMAN EMBRYOS: RETHINKING EPIGENETIC RISK BEYOND MORPHOLOGY

Abstract

Although vitrification has transformed assisted reproductive technology, it occurs during a critical developmental window characterized by extensive epigenetic remodeling and transcriptional recalibration; freeze-thaw procedures expose gametes and embryos to osmotic, cryoprotectant, oxidative, and mitochondrial stress, raising concerns about molecular effects beyond morphology. This structured narrative review, conducted without a predefined protocol, evaluates whether vitrification induces meaningful epigenetic disruption by integrating current human methylome, transcriptomic, and clinical outcome data. English-language literature was searched in PubMed/MEDLINE and Scopus, supplemented by manual screening of the reference lists of retrieved articles. Priority was given to human preimplantation embryo studies published up to January 2026, while mechanistic inferences were drawn selectively from oocyte, sperm, and animal-model data where direct human evidence was limited. Evidence derived from a limited number of primary human embryo studies generally suggests preservation of global DNA methylation architecture and overall transcriptional stability under contemporary protocols. Reported molecular alterations are predominantly localized and modest in magnitude, while available clinical data do not show a reproducible reduction in implantation or live birth rates associated with vitrification. The interaction between cryobiological stress and gamete-derived epigenetic architecture (paternal DNA methylation, chromatin organization, and small non-coding RNA cargo) may further influence embryonic sensitivity. Vitrification appears to be a biologically active yet developmentally buffered intervention; available data suggest that detectable molecular variation is generally limited rather than indicative of global epigenomic destabilization. Future stage-specific multi-omics studies integrated with longitudinal outcomes are required to define thresholds of biological relevance.