Ovarian Hyperstimulation Syndrome (OHSS)

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.

It can reach the liver, diaphragm and 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. This means that toxins that should be got rid of start to build up. The blood cells inside the arteries and veins become very concentrated and can clot or block the blood vessel. The effect of this depends on where the blood should have been going and can be very serious such as the brain. This is a type of stroke. All this means we try hard to prevent OHSS from happening in the first place and we try to treat it early if it appears to be developing.

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 having IVF 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.

Who has an increased chance of developing OHSS?

• Younger people.
• If you have polycystic ovaries or PCOS.
• If you have a high antral follicle count (AFC), or a large pool of resting follicles.
• If you have a high level of AMH (Anti-Müllerian Hormone) level your blood.
• If you have had OHSS before.
• If you are taking fertility drugs.

Sometimes OHSS does not cause symptoms until your pregnancy has implanted and pregnancy hormones are being made. This is 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 of the 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 a large number of follicles or eggs you may be advised at the time of egg collection 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. 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?

If you are thought to be at risk of developing OHSS you will be offered blood tests to measure the concentration and clotting of your blood, and the chemistry of the kidneys and occasionally the liver. Your fertility clinic will keep a close eye on you following your egg collection. You will be advised to drink according to your thirst.

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 the chart in the paper copy of this leaflet. (A PDF file of this leaflet can be downloaded at the top of this page and printed from if required).

This means we can work out whether the blood vessels are letting the fluid leak out inside your body instead of making the kidneys make urine that you can get rid off.

You will be prescribed a daily blood thinning injection 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 on an out-patient basis, provided we know of your symptoms early in the day.

Very occasionally, you may need to be admitted to the gynaecology ward at St James’s University Hospital for overnight care involving the protein drip, pain relief and sometimes to drain off some of the fluid from the tummy.

Symptoms can come and go for a few days or weeks so we will continue to see you for assessment if necessary, and keep in touch with you as you recover.

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 naturally gets better.

What to do if you think you might be getting OHSS

Please contact your fertility clinic directly to discuss your concerns and symptoms. If you become very concerned when the clinic is closed, e.g. with shortness of breath, especially coming on suddenly. you are advised to attend your local A&E department.

Glossary

• Anti-Mullerian hormone (AMH): This hormone is produced by the antral follicles and is used as one of the ways of predicting how an ovary may respond to IVF hormone stimulation. A high level indicates sensitive ovaries and the need for a lower dose of hormone stimulation.
• Antral follicle count (AFC): The number of resting follicles that are waiting to enter the final growing phase towards ovulation. This measurement is used as one of the ways of predicting how an ovary may respond to IVF hormone stimulation.
• Human Albumin Solution (HAS): A protein product extracted from human blood which is used intravenously to help prevent further leakage in OHSS and maintain normal hydration and body chemistry.
• Long IVF protocol: This is also known as an ‘agonist’ protocol where ovulation is prevented for a longer period of time and starts 10-14 days before the stimulation injections.
• Polycystic Ovary Syndrome (PCOS): A hormonal disturbance which causes subfertility mainly by causing the periods, and therefore ovulation, to become irregular. Polycystic ovaries typically have many follicles (egg sacs) waiting for the hormonal message to start growing. Sometimes too many will take off as the same time and increase the risk of OHSS developing.
• Short IVF protocol: This is also known as an ‘antagonist’ protocol where ovulation is prevented from day 6 of the stimulation injections.
• Tinzaparin: A brand of the drug Heparin which is a blood-thinning agent to prevent blood clots (thrombosis).

Contact us

Leeds Centre for Women’s Health, Gynaecology

OHSS Monitoring Program

Blood tests

You will be told by clinical staff the dates and times that blood tests and monitoring appointments are booked for.

Fluid balance chart

Please record all the fluid you drink: 1 average sized mug measures 250ml. You must also measure all the urine you pass in mls.

Method

1. Discard the first sample of urine when you get up, on the first day only.
2. From then on, you should measure the volume of each sample until the next morning.
3. The next morning you should include the volume of the first sample you pass.

This should make up the total record of fluid taken in and fluid passed out. Skip a line or two on the chart to separate each daily record and work out the total drink intake and urine output, if possible.