Two numbers, same condition, neither one lying
You've seen the clinic's number.
Under 2 percent, severe OHSS, stated flatly during intake.
Then you've seen the forum number.
One in three, sometimes higher, stated just as flatly by women who lived it.
You've already tried lining these up against each other directly, and it doesn't work.
Anecdotes and clinical stats aren't measuring the same population, or the same severity, or the same denominator.
The gap isn't a lie on either side.
It's that nobody explains what each number is actually counting.
What 1-2% is actually counting
ASRM's figure describes severe OHSS specifically.
Not mild, not moderate, just the cases that require hospitalization or intervention.
It's also typically a per-cycle rate, not a per-person one.
That distinction changes what the number means for you.
A donor who cycles three times isn't facing one 1-2% roll of the dice.
She's facing three of them, stacked.
Clinics rarely walk through that part before you sign anything.
What one in three is actually counting
HFEA's data puts mild OHSS at roughly a third of donors.
That's not a fringe forum estimate.
It's a regulator's own number, sitting next to the severe figure nobody argues about.
Forums land near this range too, though their samples self-select.
Women posting about OHSS are more likely to have had a bad reaction, which is a real selection bias worth naming.
So the forum number probably runs a little hot.
But it isn't measuring the same event as the clinic's 1-2%.
It's measuring a much wider category that clinics rarely say out loud.
Per cycle and per donor are not the same math
This is where the comparison actually breaks down.
A clinic quoting 1-2% is quoting risk per cycle, per body, per attempt.
A donor asking "what are my odds" is usually asking something bigger.
She's asking about her odds across however many cycles she'll do.
Those aren't interchangeable, and nobody flags the swap.
Run the arithmetic across cycles and a "rare" outcome looks a lot less rare.
That's a very different sentence to hear before a second retrieval.
The severity ladder nobody prints
Somewhere between "you're fine" and "you're hospitalized" sits almost nobody's paperwork.
Mild OHSS gets bloating, some pain, and gets called normal recovery.
Moderate OHSS gets weight gain, nausea, and often still gets called normal recovery.
Severe OHSS gets fluid on the lungs and an ER visit.
Consent forms tend to describe the bottom rung and the top rung.
The wide middle, where most symptomatic donors actually land, goes unlabeled.
A clinic can hand you a low number and a high number and still leave out the category most donors experience.
What the middle actually feels like
One donor described her abdomen as "the size of a basketball."
Another said her stomach "looked five months pregnant," painful to the touch.
A third described "bubbles around my collarbone" as fluid pressed against her lungs.
None of these were labeled severe on paper.
All of them were dismissed, at first, as expected recovery.
If you were told OHSS was rare during counseling, this is the part that gets skipped, the wide band of symptoms your clinic already knew could happen.
The gap between "normal" and "mild OHSS" is where donors keep getting lost.
Egg yield keeps showing up as the variable nobody explains
Donors with high retrieval counts keep reporting the roughest recoveries.
40, 50, 60-plus eggs shows up again and again in the worst accounts.
One donor learned her count was 63 only after severe symptoms started.
Another needed an ER visit the day after a 43-egg retrieval.
Correlation isn't the same as a guaranteed mechanism.
But it's a variable donors say they were never given in advance.
Nobody hands you a projected yield and lets you weigh it beforehand.
Then the second cycle changes the math again
A smooth first cycle gets read as the body "handling it well."
So a dose increase for cycle two rarely gets explained, or questioned.
Repeat donors describe an easy first round followed by a much harder second.
Some clinics attribute the harder reaction to the donor being "super fertile."
That framing moves responsibility away from the dosing decision itself.
If you're a repeat donor weighing a third cycle, this is the number worth asking for before the next dose change, not after.
If dose changes carry real risk, that's a second number donors deserve to see written down.
Right now it mostly doesn't exist on paper anywhere.
Why the simple number survives anyway
A single severe-OHSS percentage is easy to print, easy to defend, easy to quote.
A severity-by-severity, cycle-by-cycle breakdown is harder to summarize in an intake meeting.
There's also a blunter incentive sitting underneath this.
Higher egg yields serve clinics and agencies as much as they serve outcomes.
A donor asking sharper questions about denominators is a donor who might yield fewer eggs, or walk away.
That's a real tension, not a conspiracy theory.
It's also exactly the kind of tension a clean disclosure would surface, instead of hide.
Whether that tension ever shows up in an actual intake packet is a fair thing to doubt, and the doubt doesn't make the math above less true.
What better disclosure would actually list
A rigorous consent form would separate severe risk from mild-to-moderate risk explicitly.
It would state whether a number is per cycle or per donor.
It would note that GnRH-agonist trigger protocols appear to lower OHSS risk.
It would note when that protocol is used, and when it isn't, and why.
It would flag that dose increases between cycles carry their own risk profile.
None of that requires new research.
It requires clinics to print what the research already distinguishes.
The ER question you still can't get answered in advance
Even a good breakdown won't tell you when to go to the hospital.
That threshold, weight gain, breathing trouble, urine output, still isn't standardized across clinics.
Some donors call with worsening symptoms and get told to drink water.
Others get the same advice right up until hospitalization becomes unavoidable.
Nobody explains beforehand who covers that ER visit if it happens.
That silence is its own kind of underdisclosure.
A severity breakdown without a clear action threshold is still an incomplete form.
What this actually changes for someone deciding again
None of this settles whether one in three is the "real" number.
It settles that the question was framed wrong from the start.
The honest version isn't a single percentage at all.
It's a severity table, a denominator, a trigger protocol, and a dose history.
You already know how to read a methodology section.
You just haven't been handed one written for you instead of a journal.
That's the form worth asking for before you sign the next one.