OHSS, am I at risk?

Ovarian hyperstimulation syndrome

Lady clutching stomach in pain OHSS

What is it?

Ovarian hyperstimulation syndrome (easy for you to say!) is a potentially serious complication of fertility treatment, particularly in vitro fertilisation (IVF).

What causes it?

Fertility drugs, usually gonadotrophins, are used to stimulate the ovaries during IVF treatment to make eggs grow. Sometimes your system may be sensitive to these drugs and it may produce an excessive response, generating “too many” follicles, leading to OHSS.

The cause isn’t fully understood, although it has become clear that a high level of human chorionic gonadotropin (hCG) — a hormone usually produced during pregnancy — in your system plays a role.

During fertility treatments, hCG may be given as a “trigger” so that a mature follicle will release its egg. OHSS usually happens within a week after you receive an hCG injection. If you become pregnant during a treatment cycle, OHSS may worsen as your body begins producing its own hCG in response to the pregnancy.

Ovarian blood vessels react abnormally to hCG and begin to leak fluid. This fluid swells the ovaries, fluid from the blood vessels leaks into your abdomen and in severe cases into the space around the heart and lungs.

Who is most likely to get OHSS?

It occurs in women who are very sensitive to the fertility medication taken to increase egg production. Too many eggs develop in the ovaries, which become very large and painful.

The risk tends to be higher in women who:

  • Polycystic ovary syndrome
  • Large number of follicles
  • Age under 30
  • Low body weight
  • High or steeply increasing level of estradiol (estrogen) before an HCG trigger shot
  • Previous episodes of OHSS

In these circumstances you’re more likely to overstimulate and produce more follicles. However, in some cases, OHSS affects women who have no risk factors at all.

How long does it last?

Most of your symptoms should resolve in 7–10 days. If your fertility treatment does not result in a pregnancy, OHSS usually gets better by the time your next period starts. If you become pregnant, OHSS can get worse and last up to a few weeks or longer.

Image of OHSS ovaries

Symptoms of OHSS?

There are three levels of seriousness:

Mild and Moderate (up to 33% of women who do IVF):

Bloating/swelling, abdominal discomfort, nausea/vomiting, cramps and heartburn/indigestion caused by a mild or moderate build-up of fluid in your abdomen and enlarged (or ‘stretched’) ovaries. Your stomach may be distended.

You experience mild weight gain caused by the fluid build-up (but less than 1kg per day).

Severe to critical: (1 to 2% of patients will experience severe forms of OHSS, with 1 in 1000 cycles the patient needs hospitalisation):

You have so much fluid that it continues travelling up your body and ends up interfering with your diaphragm’s ability to move – making breathing difficult.

The pressure from all the fluid makes your stomach feel incredibly bloated, “full” and painful. Your stomach will probably be distended.

Your blood volume decreases as a result of all the fluid leakage, which in turn might cause the kidneys to slow down their production of urine. Decreased urine output (defined as less than 30 ml of urine per hour) is considered a pretty serious symptom of OHSS.

Your blood viscosity increases as a result of the fluid portion leaking through the capillaries, leaving the cellular portion highly concentrated. This can put you at risk of blood clots in the veins and lungs (thrombosis).

Your ovaries stretch more than 12cm in response to the overstimulation, which brings about severe abdominal discomfort, pronounced bloating/swelling, heartburn/indigestion, cramps and nausea/vomiting.

You feel weak and faint because of the reduction in circulating blood volume.

You experience significant weight gain caused by the fluid build-up (approximately 1kg per day+)

When should you seek medical advice?

Call for medical help if you develop any of the symptoms of OHSS, particularly if the pain is not getting any better or if you start to vomit, have urinary problems or chest pain or have difficulty breathing.

You should have the details of your fertility unit to call for help and advice.

When does it happen?

OHSS generally develops in the week after egg collection (early onset OHSS) but you can also get symptoms after a successful fresh embryo transfer (late onset OHSS). Both of these are related to the levels of the hCG hormone in your system.

The reason you get late onset OHSS? Because after the hCG has just surged through your system thanks to the trigger injection, you get another hefty dose of the stuff, this time produced naturally by your body when you become pregnant.

How can I prevent it?

In summary, you can’t. BUT your clinic can try its best to prevent this complication for you. It’s important to note that OHSS is an uncommon and typically mild complication of IVF treatment. Treatment protocols are designed to reduce risk of severe symptoms in patients at risk.

One method of preventing OHSS involves withholding the hCG trigger entirely, a process known as cycle cancellation. This is because of the theory that hCG is strongly linked to the development of OHSS. In addition, withholding daily gonadotrophins prior to the hCG medication in IVF cycles (a technique called coasting) has also been used to reduce the risk of OHSS.

Clinics will also monitor you closely using scans and blood tests.

If I get OHSS, how can I stop it?

Put simply, you can’t. There’s nothing you can do to “cure” OHSS. The good news though is that the condition is “self-limited”: it’ll run its course as the hCG leaves your system, which usually takes around two weeks. If you’re pregnant and you have late onset OHSS, your symptoms too will be self-limited; it’s just that it’ll take a lot longer because it takes longer for the hCG to leave your system.

That’s not to say you won’t need monitoring and/or treatment, just that it’ll definitely go away at some point soon of its own accord.


Don’t panic! This doesn’t affect everyone. However, being aware of the symptoms and listening to your clinic’s advice will help your journey go as smoothly as possible. Your clinic is very experienced and will be able to guide you through everything. They will be monitoring you and will be on hand to help if you should happen to experience OHSS. You can find out the official information on OHSS on the NHS website.

Thanks to theduff.co.uk and mayoclinic.org

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