Ovarian Hyperstimulation Syndrome (OHSS)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated July 27, 2026

Ovarian hyperstimulation syndrome (OHSS) is an iatrogenic complication of ovarian stimulation protocols used in ART, in which pharmacologically elevated gonadotropin levels cause the ovaries to produce an excessive number of follicles that, on exposure to human chorionic gonadotropin (hCG), release vascular endothelial growth factor and other mediators that make capillaries leaky, triggering systemic vascular and fluid changes that range in severity from mild bloating to life-threatening thromboembolism.¹ Mild OHSS is common. Severe OHSS requires hospitalization and can involve ascites, pleural effusion, hemoconcentration, and renal impairment. The condition has historically been classified by grade,² and current major professional society guidelines address its prevention and management.¹

Women with PCOS face the highest OHSS risk because their ovaries contain large numbers of antral follicles that respond aggressively to exogenous stimulation. The antral follicle count that defines PCOS ovarian morphology is the same feature that predicts exaggerated response to gonadotropins. OHSS risk should be part of any informed consent discussion for women with PCOS who are offered ART. Both partners need accurate risk information before proceeding.

OHSS is overwhelmingly a complication of the high-dose superstimulation protocols used in ART, where the goal is to recruit as many follicles as possible for retrieval. NaProTechnology, NeoFertility, and related restorative approaches use low-dose hormonal support calibrated to documented cycle deficiencies, not pharmacologic superstimulation. OHSS risk in restorative protocols is far lower as a result. Any ovulation-induction cycle using gonadotropins still carries some risk of OHSS, rarely even with clomiphene citrate, and OHSS has occurred without any stimulation at all. This is precisely why clinicians running gonadotropin cycles within NaProTechnology and other restorative protocols monitor them by serial transvaginal ultrasound. The goal is to catch an exaggerated response early and to support the cycle the patient already has, not to replace it with an artificially driven one.

For women with PCOS and anovulatory cycles, the more fundamental question is whether the hormonal and metabolic contributors to anovulation have been identified and addressed before stimulation for ART is considered. Cycle-charting data, including sonographic ovulation classification and hormonal profiling from follicle maturation monitoring, can document ovulatory function precisely. Many women with PCOS who receive targeted metabolic and hormonal support achieve natural conception without the stimulation pathway that carries OHSS risk.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.