The Leeds Teaching Hospitals NHS Trust

Ovarian Hyperstimulation Syndrome (OHSS)

This page explains what ovarian hyperstimulation syndrome (OHSS) is, why it is important to understand if you are having fertility treatment, and how to get help if needed.

What is OHSS?

Ovarian hyperstimulation syndrome can develop when too many follicles (sacs containing the eggs) grow as a result of the hormone injections used in fertility treatments. The main symptoms are:

  • Swelling and discomfort in the tummy due to enlarged ovaries and retained fluid.
  • Sickness and loss of appetite.
  • Diarrhoea.

    Why is OHSS important to identify and treat?

    When OHSS is severe, or not treated early, it can cause serious complications. Changes in the body’s chemistry allow the fluid that normally carries the blood cells around the arteries and veins to leak out and build up in the abdomen around the ovaries, intestines and kidneys. The swelling can be painful and can reach the liver, diaphragm and collect around the lungs and heart. This can make breathing uncomfortable and cause shortness of breath. The kidneys can stop working properly and make very little urine. The blood becomes more concentrated and therefore more likely to cause clots. 

How common is it?

OHSS is much less common now than it was 10 years ago because our understanding has improved with research into the condition and especially in ways to prevent or reduce the chance of it happening.

Almost everyone gets a mild version of it which settles within a couple of days. Some people, 3-8% can get a moderate form. Fewer than 2% require admission to hospital. It usually happens to women who are having IVF but can happen after ovulation induction treatment.

 It is important to recognise that any woman using fertility drugs is at some risk of OHSS. Sometimes OHSS does not cause symptoms until the pregnancy has implanted and pregnancy hormone is being made, from about a week after your embryo has been transferred.

What causes OHSS?

Chemicals produced from over-stimulated ovaries cause the blood vessels to leak fluid and this increases the risk of blood clots.

What should you look out for?

  • Swelling and discomfort in your tummy that does not seem to be getting better or is clearly getting worse since your egg collection or embryo transfer. 
  • Dark urine and less urine than you would expect from the amount of fluid you have been drinking. 
  • Nausea, sickness and / or diarrhoea. Shortness of breath.

    How is OHSS prevented?

    If you have been found to have any risk factors listed above, the dose of hormones prescribed to make your ovaries produce multiple eggs will be modified and reduced. You will be scanned earlier and the dose changed mid-cycle if necessary, up or down. ‘Short protocols’ rather than ‘long protocols’ allow your treatment to be tailored more finely to your needs in real- time. Please ask your Consultant or Nurse Practitioner if you want to know more about this. Very occasionally, the ovaries will respond excessively quite early in the treatment. In this situation the treatment may be stopped and restarted with a lower dose injection. If you produce more than 30 eggs at the time of egg collection we will advise you that all the embryos that result from fertilisation should be frozen. This will allow you and your ovaries to recover without the risk of a pregnancy pushing the syndrome from moderate to severe. Pregnancy rates from frozen-thawed embryos are similar to fresh embryos in modern programs such as the one at Leeds Fertility. Some research is emerging to suggest that pregnancy rates are better when the body has restored its normal chemistry and the blood vessels are no longer leaky, so there may be an advantage to putting the transfer off for a few weeks.

How is OHSS treated?

When a woman is judged to be ‘at risk’ of developing OHSS she will have blood tests to measure the concentration and clotting of the blood, and the chemistry of the kidneys and occasionally the liver. Leeds Fertility will keep a close eye  on you following your egg collection with a face-to-face examination on the third and fifth days after your collection. You will be advised to drink according to your thirst. You should not force yourself to drink excessively.

  • You can take paracetamol regularly (1g every 4 hours) for pain relief. You should measure as far as is possible, what fluid you drink and what urine you pass and record it on a chart. 
  • You will be prescribed a daily injection (Tinzaparin) to keep the blood a bit thinner than normal to reduce the risk of it clotting inside the blood vessels, until the treatment cycle outcome is clear.
  • If your symptoms get worse, we may need to give you a protein drip (20% Human Albumin Solution) into a vein to keep the blood flowing and draw some of the fluid back inside the blood vessels.

This can be done at Leeds Fertility on an out-patient basis, provided we know of your symptoms early in the day.

Very occasionally, women need to be admitted to the Leeds Centre for Women’s Health (Gynaecology ward) at St James’s Hospital for overnight care involving the protein drip, pain relief and sometimes to drain off some of the fluid from the tummy.

If your symptoms develop around or after a positive pregnancy test, it can take a bit longer to get better. The condition does not harm the pregnancy or increase the risk of miscarriage. The treatments are also safe in pregnancy: they are mainly to relieve the symptoms until the condition burns itself out.

What to do if you think you might be getting OHSS

Please contact Leeds Fertility on 0113 206 3102 during office hours to discuss your concerns and symptoms. We may need to see you so calling earlier in the day (08.00) is helpful.

If you become very concerned when the clinic is closed, e.g. with shortness of breath, especially coming on suddenly,you should call the switchboard on 0113 243 3144 and ask to speak to the nurse holding the Leeds Fertility emergency phone.

You will probably be advised to attend your local emergency department. We will be able to keep in touch with the doctors looking after you to help with your care if we know that you have been admitted, and where.