OHSS Risk Score Calculator

Ovarian hyperstimulation syndrome (OHSS) is the most significant complication of controlled ovarian stimulation in IVF. Mild OHSS is common, affecting roughly 20 to 30% of cycles, and settles on its own. Moderate to severe OHSS runs at about 1 to 3% and involves substantial ovarian enlargement, fluid shifts, electrolyte abnormalities, and rarely thromboembolic or respiratory complications.

Identifying high-risk patients before stimulation is what makes prevention possible. Lower starting doses, antagonist protocols, a GnRH agonist trigger instead of hCG, and freeze-all strategies all reduce the risk substantially, and all of them have to be decided before or during the cycle rather than after.

This calculator combines the most consistently reported predictors from reproductive medicine literature into a simple additive score.

Risk factors and weights:

Age under 30: +2 (younger patients have higher ovarian responsiveness) Age 30-34: +1 Age 35 or older: 0

BMI under 25: +1 (lean patients metabolize stimulation drugs differently)

PCOS diagnosis: +2 (the strongest single demographic predictor)

AMH > 3.5 ng/mL: +2 AMH 2.0-3.5 ng/mL: +1

Antral follicle count > 20: +2 AFC 12-20: +1

Previous OHSS: +2 (recurrence risk is real even with protocol changes)

Peak estradiol > 3500 pg/mL on day of trigger: +2 (cycle-specific marker) Peak estradiol 2500-3500 pg/mL: +1

Mature follicles (>= 14 mm) > 18 on day of trigger: +2 14-18 follicles: +1

Maximum score is 15 when every factor is assessed.

Score interpretation:

• 0-2 points, low risk. A standard stimulation protocol is generally acceptable.
• 3-5 points, moderate risk. Consider an antagonist protocol and lower doses, and monitor closely for fluid shifts.
• 6-9 points, high risk. Strongly consider a GnRH agonist trigger, a freeze-all approach, and cabergoline prophylaxis.
• 10 or more, very high risk. Freeze-all is generally indicated, and cycle cancellation or coasting may be discussed.

Four of these factors are optional, and that changes how the score reads

AMH, antral follicle count, peak estradiol and mature follicle count are worth 2 points each and any of them can be left blank. Two of the four only exist on the day of trigger, so before stimulation they simply cannot be filled in.

The consequence is worth stating plainly: a score of 7 built from all eight factors and a score of 7 built from four of them are not the same result. The second one is 7 out of a possible 7, with 8 points never in play. This calculator reports the maximum that was actually reachable alongside the score, and names which factors were skipped.

It also distinguishes the two uses. Before stimulation you get a baseline prediction from patient characteristics and ovarian reserve. On the day of trigger, peak estradiol and the mature follicle count are the two strongest cycle-specific predictors in the set, and adding them is what turns a prediction into a measurement of how the cycle actually went. Running it at both points is more useful than running it once.

Limitations

This is an educational composite of predictors that recur across the reproductive medicine literature, not a validated single-tool prediction model. Real-world assessment also weighs protocol history, response to prior cycles, lab kinetics through stimulation, and the clinician’s knowledge of the individual patient.

The most effective risk reduction in modern IVF is the freeze-all approach in high-risk patients. It essentially eliminates severe late-onset OHSS, because that form is driven by the hCG rise of an established pregnancy, and a frozen transfer in a later cycle removes it entirely.