Ovarian hyperstimulation syndrome (OHSS)

Ovarian hyperstimulation syndrome is a potentially serious complication of fertility treatment, particularly of in vitro fertilization (IVF).

What are the symptoms of OHSS?

OHSS can range from mild to severe:

• Mild OHSS – mild abdominal swelling, discomfort and nausea.
• Moderate OHSS – symptoms of mild OHSS, but the swelling is worse because of fluid build-up in the abdomen. This can cause abdominal pain and vomiting.
• Severe OHSS – symptoms of moderate OHSS with extreme thirst and dehydration. You may only pass small amounts of urine which is dark in color and/or you may experience difficulty breathing because of a build-up of fluid in your chest. A serious, but rare, complication is formation of a blood clot (thrombosis) in the legs or lungs. The symptoms of this are a swollen, tender leg or pain in your chest and breathlessness.

What causes OHSS?

Fertility drugs, usually gonadotrophins, are used to stimulate the ovaries during IVF treatment to make eggs grow. Sometimes there is an excessive response to these drugs, leading to OHSS. Overstimulated ovaries enlarge and release chemicals into the bloodstream. Fluid from the blood vessels 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 very small number of deaths due to OHSS have been reported.

Who gets OHSS?

OHSS is just over 1 in 100 women (1%).

The risk is higher in women who:

• Have polycystic ovaries
• Are under 30 years old
• Have had OHSS previously
• Get pregnant in the same IVF cycle as they get their symptoms, particularly if this is a multiple pregnancy (more than one baby).

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.

What should I do if I have mild OHSS?

If you have mild OHSS, you can be looked after at home. Ensure that you drink fluids at regular intervals depending on how thirsty you feel. If you have pain, take paracetamol or codeine (no more than the maximum dose). You should avoid anti-inflammatory drugs (aspirin or aspirin-like drugs such as ibuprofen), which can affect your kidneys. It is advisable to remain active to reduce the risk of thrombosis.

When should I call for medical help?

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.

What may happen at the hospital?

Your doctor will ask you to describe your symptoms and will examine you.

• Ask about how much urine you are passing and whether it is darker than normal
• Measure your blood pressure, pulse rate and breathing rate
• Take an initial measurement of your waistline and check your weight to see whether the fluid is building up or reducing 3
• Arrange an ultrasound scan to measure the size of your ovaries and to check whether there is any fluid build-up in your abdomen
• Take blood tests to measure how concentrated your blood is and how well your kidneys are working.

What is the treatment for OHSS?

Treatment is to help symptoms and prevent complications.

• Pain relief such as paracetamol
• Anti-sickness drugs to help reduce nausea and vomiting
• An intravenous drip to replace fluids
• Support stockings and heparin injections to prevent thrombosis. Heparin injections for blood thinning should be continued for 7 days from cure of your symptoms if you are not pregnant or until the end of the 12th week of your pregnancy. If your abdomen is tense and swollen because of fluid build-up, you may be offered a procedure known as a paracentesis. This is when a thin needle or tube is inserted under ultrasound guidance into your abdomen to remove fluid. You may be offered a local anaesthetic for this procedure. This treatment helps relieve discomfort and improve kidney function and your breathing. Rarely, advice may be sought from a more specialist team which may involve anaesthetists and/or intensive care doctors.