What is OHSS?

Ovarian hyperstimulation syndrome (OHSS) is a potentially serious complication of IVF treatment. Although the majority of patients will not experience OHSS, it’s important to be aware of the condition and the symptoms to look out for.


What are the symptoms of OHSS?

The symptoms of OHSS are abdominal swelling or bloating because of enlarged ovaries, nausea and, as the condition gets worse, vomiting.

  • Mild OHSS – Mild abdominal swelling or bloating, abdominal discomfort and nausea. Most patients have some of these symptoms following IVF and should not be too worried.
  • Moderate OHSS – symptoms of mild OHSS but the swelling and bloating is worse because fluid is building up in the abdomen. There can be abdominal pain and vomiting. There may be reduced urine output and tightness of the chest when taking a large breath.
  • Severe OHSS – symptoms of moderate OHSS plus extreme thirst and dehydration because so much fluid is building up in the abdomen, passing very small amounts of urine which is very dark in colour (concentrated). Shortness of breath can be experienced because of build-up of fluid in the chest. Rarely a red, hot, swollen and tender leg due to a clot in the leg or lungs (thrombosis).


What causes it?

Drugs are given to stimulate the ovaries to produce follicles.

Sometimes there is an excessive response to fertility drugs, and this causes OHSS. Overstimulated ovaries enlarge and release chemicals into the bloodstream that make blood vessels leak fluid into the body. Fluid leaks into your abdomen and, in severe cases, into the space around the heart and lungs. OHSS can affect the kidneys, liver, and lungs. A serious, but rare, complication is a blood clot (thrombosis). A very small number of deaths have been reported.


Who gets it?

Mild symptoms are common in women having IVF treatment.

About 3 – 5% women will develop moderate or severe OHSS.

OHSS can affect anyone undergoing IVF, however, the risk of OHSS is increased in women who:

  • have polycystic ovaries.
  • are under 30 years.
  • have had OHSS previously.
  • get pregnant with the above risk factors, particularly if this is a multiple pregnancy (twins or more).


How long does OHSS last? 

  • Most of the symptoms should usually resolve in a few days with mild OHSS and the patient can be looked after at home.
  • If the IVF treatment does not result in a pregnancy, OHSS will get better by the time the period starts.
  • If the IVF treatment results in a pregnancy, OHSS can get worse and last up to a few weeks or longer.


What is the treatment for OHSS?

There is no treatment that can reverse OHSS.

OHSS will get better with time, so treatment is to help symptoms and prevent further problems. This includes:

  • regular blood tests to monitor the condition. This may be performed at the IVF Clinic as an outpatient.
  • encourage regular drinks of clear fluids to ensure you remain hydrated.
  • pain relief such as paracetamol or codeine
  • anti-sickness drugs to help reduce nausea and vomiting.
  • an intravenous drip to rehydrate you.
  • support stockings and heparin injections to prevent a clot developing in the leg or lungs (thrombosis)
  • Admission to hospital for assessment is sometimes required in moderate to severe cases.


Is my baby at risk if I have OHSS?

There is no evidence of problems in the baby as a result of OHSS.