Ovarian hyperstimulation syndrome (OHSS) is a condition classified based on symptom severity along with laboratory test values into mild, moderate, severe, or critical stages. It can also be categorized by onset: primary or early-onset, which manifests within 8 days post-trigger injection—often linked to high-dose hCG—and secondary or late-onset, appearing between 9 and 13 days after the trigger, typically associated with pregnancy-related hCG in fresh embryo transfer cycles. A rare form, spontaneous OHSS, occurs during pregnancy and may be associated with multiple gestations, molar pregnancies, or hypothyroidism, usually between 8 and 14 weeks of gestation. Both severe and critical cases demand intensive management, including hospitalization and procedures like paracentesis. The underlying pathophysiology involves capillary leakiness caused by increased permeability, leading to fluid shift from the vascular system to third spaces, which is now considered a form of compartment syndrome. Vascular endothelial growth factor (VEGF) and hCG—either exogenously administered or produced endogenously—are key mediators, though many aspects of the mechanisms remain unclear. Preventive strategies focus on identifying high-risk groups, such as individuals with polycystic ovary syndrome (PCOS), elevated ovarian reserve markers (AFC and AMH), multiple oocyte retrievals, prior OHSS episodes, or multiple pregnancies. Iatrogenic causes linked to hCG triggers and random ovulation induction have led to individualized ovarian stimulation protocols. Approaches like GnRH antagonist protocols, switching to GnRHa triggers, embryo cryopreservation, and double triggers with low-dose hCG are employed to mitigate risks. Additionally, routine use of medications such as cabergoline and metformin, or novel triggers like kisspeptin, is proving effective. Some centers add IV calcium or utilize follitropin delta stimulation, which maintains efficacy without increasing clinical pregnancy rates. There are outcome studies that link OHSS with preterm birth and low birth weight, emphasizing prevention. The goal is to transition to an “OHSS-free” model, where prophylactic protocols reduce the syndrome’s occurrence, making it a part of history rather than a future concern.