Empty Follicle Syndrome: Current Therapeutic Approaches and the Role of Triggering Agents in Assisted Reproductive Technology.

The hallmark feature of empty follicle syndrome (EFS) is failure to retrieve oocytes from apparently mature follicles despite adequate ovarian stimulation and appropriate ovulation triggering. Although considered uncommon, with a reported prevalence ranging from 0.2% to 7%, EFS may have a profound clinical and psychological impact and can recur in assisted reproductive technology (ART) cycles. Modern classification systems divide EFS into genuine and false forms. Genuine EFS is potentially associated with intrinsic abnormalities involving luteinizing hormone/choriogonadotropin receptor (LHCGR) signaling, oocyte competence, and cumulus-oocyte interaction, whereas false EFS is primarily attributed to pharmacokinetic or pharmacodynamic factors resulting in inadequate trigger exposure. Borderline EFS represents a third phenotype characterized by incomplete or partial impairment of final oocyte maturation. This review examines the pharmacodynamics of ovulation-triggering agents, including human chorionic gonadotropin (hCG), gonadotropin-releasing hormone (GnRH) agonist protocols, and dual-trigger strategies, and their roles in regulating final oocyte maturation. The molecular aspects of periovulatory signal transduction and the mechanisms of LHCGR activation, epidermal growth factor (EGF)-like pathways, and meiotic resumption in relation to EFS etiopathogenesis will be described. The impact of patient-dependent conditions like obesity, poor ovarian reserve, polycystic ovary syndrome (PCOS), and pituitary response on trigger response will be assessed. New approaches like post-trigger monitoring of hormones and rescue treatment with gonadotropins represent a valuable method for avoiding cycle cancellation in patients at risk. Overall, EFS is increasingly regarded not as a single disorder but as a heterogeneous spectrum of periovulatory dysfunction arising from pharmacological, endocrine, and intrinsic ovarian factors that impair completion of final oocyte maturation.