OHSS: Symptoms, Warning Signs and Prevention

Ovarian hyperstimulation syndrome (OHSS)

OHSS is the main serious complication of ovarian stimulation. Most cases are mild. It is largely preventable, and prevention has improved substantially in recent years.

This page is mainly about recognising it, because that is the part that depends on you.

Warning signs — contact your clinic the same day

Do not wait for your next appointment, and do not wait to see if it settles overnight.

• Severe or worsening abdominal pain
• Marked bloating — clothes not fitting, abdomen visibly distended
• Nausea or vomiting
• Breathlessness, or difficulty lying flat
• Reduced urine output — passing much less than usual
• Rapid weight gain — more than about a kilogram in 24 hours

Weighing yourself daily after egg retrieval is a simple and useful thing to do. Rapid weight gain is often the earliest objective sign, and it appears before you feel seriously unwell.

Also seek urgent care for

• Fever
• Heavy vaginal bleeding
• Sudden severe one-sided pain — the ovaries are enlarged after stimulation and ovarian torsion is a recognised risk

A note on calling

Many people delay because they do not want to seem anxious or to bother the clinic out of hours. Clinics expect these calls and would far rather assess someone who turns out to be fine than see someone late.

If you are wondering whether your symptoms warrant a call, that is itself a reason to call.

Who is at higher risk

• Younger women
• PCOS — now renamed polyendocrine metabolic ovarian syndrome (PMOS)
• High antral follicle count or high AMH
• Previous OHSS
• A large number of follicles developing in the current cycle

ESHRE (2026) recommends a risk assessment for high response before starting stimulation, so that the suppression protocol, gonadotropin dose, trigger and transfer strategy can all be individualised.

If you have any of the risk factors above, it is reasonable to ask what specifically has been adjusted in your protocol.

How it is prevented

The recommendations here are among the strongest in the ESHRE guideline.

GnRH antagonist protocol for predicted high responders — strong recommendation.

Reduced gonadotropin dose, 100 to under 150 IU — probably recommended for predicted high responders, specifically to decrease OHSS risk.

GnRH agonist trigger combined with freeze-all — recommended to minimise the risk of severe OHSS. Strong recommendation, and the single most effective preventive step.

Dopamine agonists — recommended to decrease the risk of early OHSS, particularly where hCG is used for final oocyte maturation. Strong recommendation, and new in the 2026 update.

Freeze-all strategy — recommended to minimise late-onset OHSS. Strong recommendation.

Where a GnRH agonist protocol produces 19 or more follicles of 11 mm or greater, preventative measures are recommended, primarily cancelling the trigger.

What is not recommended

Adding hCG to a GnRH agonist as a dual trigger in high responders. And a GnRH agonist trigger, with or without freeze-all, is preferred over coasting.

If your cycle is cancelled

Having a trigger cancelled after days of injections is genuinely disappointing, and it can feel like the cycle was wasted.

It was not. The decision is made to protect you from a condition that can become serious, and the eggs are not lost — a subsequent cycle can be planned with a modified protocol, a lower dose, and a different trigger strategy.

A cancelled cycle is a clinic doing its job.

Early and late OHSS

Early OHSS develops within about a week of the trigger, driven by the trigger injection itself. This is what dopamine agonists and the agonist trigger address.

Late OHSS develops later and is driven by pregnancy hormones. This is why a freeze-all strategy helps — with no fresh transfer, there is no pregnancy in that cycle to sustain it.

If you conceive in a fresh transfer cycle and develop symptoms, tell whoever assesses you that you have had IVF and may be pregnant. Symptoms can worsen as pregnancy progresses.

Recovery

Mild cases settle over days to a couple of weeks. Moderate and severe cases need monitoring and sometimes admission for fluid management.

Rest, adequate fluid intake and monitoring your weight are the usual advice for mild cases — but follow your own clinic's instructions, and do not manage worsening symptoms at home.

Questions worth asking before you start

• Am I at higher risk of OHSS, and what has been adjusted in my protocol because of it?
• What trigger are you planning, and why?
• Are you planning a fresh transfer or a freeze-all?
• Who do I call out of hours, and what number?

That last one is the most practical thing on this page. Have the out-of-hours number saved in your phone before your retrieval, not after symptoms start.