Ovarian Hyperstimulation Syndrome (OHSS) is a serious, exaggerated response to the injectable hormone medications used during fertility treatments, such as in vitro fertilization (IVF). The condition causes the ovaries to become swollen and painful, often leading to a shift of fluid from blood vessels into the abdominal cavity. This fluid shift can result in significant discomfort and, in severe cases, life-threatening complications like blood clots and organ failure. The primary driver of this reaction is the human chorionic gonadotropin (hCG) hormone, which is administered as a “trigger shot” to finalize egg maturation and is also produced naturally during pregnancy. Because OHSS can range from mild to severe, a multi-faceted approach focused on prevention throughout the entire treatment cycle is necessary to ensure patient safety.
Recognizing Individual Risk Factors
Identifying a patient’s predisposition to an exaggerated ovarian response is the first step in creating a safer treatment plan. Patients with Polycystic Ovary Syndrome (PCOS) are at a substantially elevated risk due to their large reserve of small follicles. Other risk factors include being under 35, having a low body mass index (BMI), or a history of a previous OHSS episode. Clinicians use specific markers to quantify ovarian reserve, such as Antral Follicle Count (AFC) or Anti-Müllerian Hormone (AMH) level. An AFC of 24 or more or an AMH level over 3.36 ng/mL indicates a significantly higher risk profile. Recognizing these individual factors allows medical teams to tailor a personalized stimulation protocol from the outset.
Pharmacological Strategies During Stimulation
The choice of medication protocol during the ovarian stimulation phase is a powerful tool for avoiding OHSS, particularly in high-risk individuals. Gonadotropin-releasing hormone (GnRH) antagonist protocols are generally preferred over the older GnRH agonist protocols for high-risk patients because they offer greater flexibility in managing the final trigger shot. Clinicians apply the principle of “start low and go slow” to the daily dose of injectable gonadotropins, tailoring the dose based on the patient’s AMH level and AFC. This aims to achieve sufficient mature eggs without inducing an excessive ovarian response. The most important strategy involves the trigger shot. Since the standard hCG trigger causes severe OHSS due to its long half-life and sustained ovarian stimulation, a GnRH-agonist trigger (e.g., Leuprolide) is used for high-risk patients instead. This trigger induces a rapid, short-lived surge of luteinizing hormone (LH) that matures the eggs but clears quickly, eliminating severe OHSS risk. However, this necessitates a “freeze-all” approach, as the short-acting trigger severely compromises the uterine lining’s ability to support a pregnancy.
Monitoring and Cycle Adjustments
Close, real-time monitoring is essential during the ovarian stimulation phase. Frequent transvaginal ultrasounds count and measure developing follicles; the presence of 15 or more follicles often serves as a warning sign. These scans are paired with regular blood tests to measure serum estradiol (E2) levels, which rise rapidly as follicles grow and can predict the severity of a potential hyperstimulation event. If E2 levels climb too high or too many follicles develop, the medical team can implement a temporary strategy called “coasting.” Coasting involves temporarily withholding the gonadotropin injection until the E2 level decreases. This adjustment allows smaller follicles to regress while larger ones mature. In rare cases of extremely exaggerated response, the safest preventative action is to cancel the cycle entirely before the trigger shot, which completely avoids the risk of OHSS.
Post-Retrieval Mitigation Techniques
Strategies are employed after egg retrieval to ensure OHSS does not develop or progress into a severe form. The most impactful strategy is the “freeze-all” approach, mandatory when a GnRH-agonist trigger is used. All viable embryos are cryopreserved, delaying transfer until a later, non-stimulated cycle. This prevents “late OHSS,” which is severe and prolonged, because it avoids the introduction of pregnancy-related hCG that would sustain the hyperstimulation reaction. Supportive measures include maintaining high fluid intake with electrolyte-rich beverages to combat the fluid shifts and potential dehydration. Doctors may also prescribe Cabergoline, a dopamine agonist, which reduces OHSS severity by targeting the mechanism causing fluid leakage.