OHSS

OHSS is ovarian hyperstimulation syndrome, the main risk of the drugs used to grow eggs. The ovaries over-respond, they leak fluid out of the bloodstream into the abdomen, and in the severe form that needs hospital treatment. Mild bloating after egg collection is expected. Rapid weight gain and breathlessness are not.

Where you'll meet it

On the consent form before an IVF or egg freezing cycle, and in the safety talk from the nurse. It is the reason protocols changed over the last fifteen years, and the reason so many clinics now freeze everything rather than transferring fresh.

What happens in the body

Stimulation drugs push the ovaries to grow a cohort of follicles instead of one. In some people the ovaries respond far harder than intended. They become enlarged and start releasing substances that make small blood vessels leaky, and fluid shifts out of the circulation and collects in the abdomen, sometimes around the lungs.

That shift is what causes the symptoms. The abdomen swells, the blood left in the circulation becomes concentrated, and the combination is what makes the severe form dangerous rather than just uncomfortable. The trigger injection, and then a pregnancy if one follows, both sustain the process, which is why the timing of symptoms matters.

Mild, moderate and severe

Mild is common. Bloating, a tight abdomen, some discomfort for a week or so after collection. Uncomfortable, self-limiting, and not a complication in any meaningful sense.

Moderate adds nausea, more swelling and visible fluid on a scan, and usually means closer monitoring rather than admission.

Severe is the one the consent form is about. Significant fluid in the abdomen, breathlessness, a much reduced urine output, and a raised risk of blood clots. It is uncommon, generally quoted on the order of a percent or two of cycles, and lower again on a modern protocol. It is treatable, and it is treated far more easily when it is caught early.

Who is most at risk, and how clinics prevent it

The risk sits with strong responders. Polycystic ovaries, a high antral follicle count, a high AMH, younger age and a previous episode all raise it. Clinics look at those before choosing a dose, which is most of what ovarian reserve testing is actually for.

Prevention is now a set of habits rather than luck. An antagonist protocol allows a different trigger injection, one that empties the follicles without the long tail of hormone the standard trigger leaves behind. Freezing all the embryos and transferring in a later cycle removes the pregnancy that would otherwise keep the process going. Doses are adjusted downwards mid-cycle, and occasionally a cycle is cancelled or converted, which is disappointing and much better than the alternative.

When to pick up the phone

This is the practical part. Bloating after collection is expected. What is not expected is putting on weight quickly over a day or two, an abdomen that becomes tight and painful rather than just full, breathlessness, being unable to keep fluids down, or passing very little urine.

That combination, in the days after collection, is how the serious form announces itself. Call the clinic that evening rather than in the morning. Every unit has an out-of-hours number and they would far rather hear from you early. I have never once seen a clinic treat that call as a nuisance.

Questions to ask

Ask what your risk looks like given your reserve results, and what protocol and trigger they plan to use because of it. Ask whether they intend to freeze everything if your response is strong. And write down the out-of-hours number before the cycle starts rather than looking for it at ten at night with a swollen abdomen.

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