The Leeds Teaching Hospitals NHS Trust


Ovarian Hyperstimulation Syndrome (OHSS)


What is ovarian hyperstimulation syndrome?

This is a condition where ovaries over respond to the hormone injections used to stimulate the growth of the follicles that contain the eggs. This is categorised by:

  1. Ovarian enlargement with more than the average number of follicles.
  2. Fluid accumulation - most commonly in abdomen and rarely around the lungs and heart.

As a result of the shift of fluid out of the circulatory system to principally the abdominal cavity there is an increased risk of these rare complications.

How common is OHSS?

This can occur in 1% - 10% of patients undergoing IVF treatment. Approximately 1 in 100 to 1 in 200 patients will need short stay in the hospital because of hyperstimulation.

Who is at risk?

  • Anyone undergoing treatment with fertility drugs is ‘at risk’
  • This complication occurs most commonly:

          In those patients who have had IVF or ICSI treatment.

          Patients with polycystic ovaries (PCO).

          Very young patients (less than 30 years).

  • Occurrence is related to the total number of follicles present in the treatment cycle.
  • Risk is increased in patients with increased number of follicles who subsequently become pregnant.

What causes OHSS?

OHSS is due to chemicals produced by the follicles which then cause leakage of fluid into the abdominal cavity and reduces the circulating fluid in your blood vessels. Untreated, it may result in:

  • thickening of the blood which interferes with its circulation and may start to form clots and there is also a risk that these may travel elsewhere (embolism), for example to the lungs or the brain.
  • The reduction in circulating fluid volume can cause impaired blood flow to kidneys and reduce urine output.
  • Sudden breathlessness has also been reported as a result of OHSS.

It is therefore a very serious condition which we try to ensure is recognised in very early stages, is monitored and treated accordingly.

What are the symptoms of OHSS?

The warning symptoms are thirst, nausea (feeling sick), abdominal pain, abdominal bloatedness, shortness of breath, vomiting, diarrhoea and general malaise.

How can this be prevented?

Your treatment cycle is carefully planned to keep the risk of OHSS to a minimum by selecting the most appropriate dose of medication to stimulate the ovaries. As overall only 60% eggs fertilise, 80-90% grow and as there is a difference between the growth potential of embryos formed, we do need a certain number of eggs to start with in order to be able to give you a good chance of success. Women with PCO also have a threshold below which they do not respond and above which they respond excessively ‘the all or none phenomenon’.

It is therefore a careful balancing act to give you adequate stimulation for both too little and too much could be detrimental to you and your treatment success rate.

We do monitor you very closely during the course of treatment to adjust the dose of medication.

  • If the ultrasound scan shows too many follicles developing the treatment cycle may be cancelled before we get to the egg collection.
  • We may recommend freezing all embryos resulting from that IVF cycle to be put back at a later date as we know that a pregnancy can significantly increase the severity of OHSS.
  • As part of monitoring and early detection of problems, blood samples will be taken to have a baseline assessment on the day of your egg collection and periodically thereafter.
  • We will also teach you how to monitor your fluid intake and output at home for review with us after the egg collection, usually twice a week.
  • We give subcutaneous injection given to prevent thickening of blood leading to clotting. This is a prophylactic measure.

If we think you may be at risk, we will advise you. There are some measures you can then take to reduce the symptoms of OHSS, as follows:

  • We advise you to maintain your normal oral intake of fluids and food. Please feel free to drink what ever you like and whenever you like but you do not have to force yourself to drink more than what you want.
  • Watch the amount of urine you produce – you will be given a fluid chart where you can enter the amount of fluids you take and the measure of urine you pass in 24 hours. Please report if you have not produced more than 1 litre of urine in 24 hours.

What to do if you are not well?

If you experience any of the warning symptoms you need to contact the clinic immediately, in normal working hours Mon to Fri 8.00 am – 5.00 pm on 0113 2063111, and out of hours you should contact St James’s Hospital switch board on 0113 2433144 and you can contact the LCRM duty member of the staff via the emergency mobile telephone.

You will be seen on the Unit by a doctor who will examine and assess you. A scan may be performed, you will be taught how to monitor your fluid balance at home and you will have a few blood tests to assess your blood count, blood clotting, liver function and kidney function until you are due for a pregnancy test.

In most circumstances the symptoms usually settle over a few days. We will also provide you with medication to make you feel less sick and pain killers if you are in discomfort. However when required we may:

1. give you an intravenous infusion of salt poor albumin in LCRM as a prophylactic measure
OR
2. arrange hospitalisation in our gynaecology wards at St James’s for further observation and treatment.

If you have any queries please contact the Leeds Centre for Reproductive Medicine on 0113 2063111.