• About this information

    This information is for you if you are undergoing treatment that carries a risk of ovarian hyperstimulation syndrome (OHSS) or have developed OHSS. It may also be helpful if you are a relative or friend of someone who is in this situation.

  • What is OHSS?

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

    It can also develop as side effect of the drugs used to stimulate production of eggs in fertility treatments. In the majority of patients OHSS is a mild condition but less commonly it can be serious medical complication necessitating admission to hospital for specialist treatment.

  • What are the symptoms of OHSS?

    The most common symptoms are generalised abdominal swelling and discomfort and nausea. The abdominal swelling is due partly to swelling of the ovaries as a result of their stimulation but mainly to accumulation of fluid. In more serious cases the abdominal swelling becomes marked and the woman may complain of a reduction in the amount of urine passed and breathing difficulties. 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 colour 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. You should report any unusual symptoms to your doctor.

  • 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.

    Over stimulated 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.

    Any drug used in the stimulation of ovulation has the potential to cause OHSS - even fertility tablets such as Clomiphene or Clomid although OHSS is very rare in these circumstances.

  • How likely am I to develop OHSS?

    In Vitro Fertilisation have between a 3 - 5 % chance of developing mild OHSS. Moderate and severe forms of OHSS which will require admission to hospital and specialised treatment occur in 0.1 - 2 % of cases undergoing IVF and related treatments.

  • Who can develop OHSS?

    Any woman who is given drugs to stimulate ovulation or the production of eggs. Women who are known to have Poly Cystic Ovaries are at greater risk Mild OHSS is common in women having IVF treatment; affecting as many as 33 in 100 women (33%). However, just over 1 in 100 women (1%) will develop moderate or severe OHSS.

    Other risk factors are, young age, low body weight, use of excessive amounts of gonadotrophin injections, high or rapidly rising levels of estrogen during the stimulation phase and previous episodes of OHSS. The risk is also higher if the women 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.

  • Is OHSS a dangerous condition?

    OHSS is uncommon and when it occurs is usually a mild condition with slight abdominal distension and discomfort that passes off after a week or so without requiring admission to hospital or special treatment. In some cases, however, it develops into a more serious condition requiring hospitalisation and specialist treatment. Even in these more severe cases the condition almost always resolves completely with no long-term complications or effects. Fatalities have occurred from OHSS but are exceptionally rare; in fact you are 10 times more likely to die from normal childbirth than from OHSS.

  • What is the treatment for OHSS?

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    Although there is no treatment that can reverse OHSS, it will usually get better with time. Treatment is to help symptoms and prevent complications.

    This includes:

    • pain relief such as paracetamol or codeine
    • anti-sickness drugs to help reduce nausea and vomiting
    • an intravenous drip to replace fluids
    • support stockings and heparin injections to prevent thrombosis (a blood clot in the leg or lungs). 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.

  • Are there any long term effects following OHSS?

    A complete recovery is the rule even when the condition is severe. The ovaries, which become quite enlarged with cysts, can take several weeks to shrink down but return completely to normal within 4 - 6 weeks. There is no evidence to suggest that this condition increases the likelihood of developing cancer of the ovaries in the future.

  • What about the treatment cycle?

    If there are signs of this condition developing during the stimulation part of the infertility treatment we may adjust the treatment to prevent it developing into a more serious problem. Two possible ways of reducing the likelihood of OHSS developing are:

    • Reducing the dose of drug stimulation.
    • “Coasting” the stimulation phase – this means stopping the stimulation drugs for 3-4 days before removing the eggs.Unfortunately the only certain way of avoiding OHSS is to stop the treatment. If we do this further treatment will be discussed with you and how it might be altered to reduce the chances of this happening again. Treatment can usually be started again within a few weeks after the ovaries have settled down.
  • Is it possible to prevent this problem?

    As has already been mentioned women with polycystic ovaries are more likely to develop this problem. The ovaries are scanned at the start of treatment and if they are polycystic we would normally adjust the dose of stimulation to take this into account.
During the cycle of stimulation (in vitro fertilisation), one of the purposes of monitoring is to detect signs of over response and possible developing OHSS. If this is the case we may either reduce the dosage of the stimulation, “coast” the treatment – stop the drugs for several days, or even abandon the treatment. The monitoring will be with ultrasound scans to assess the development of the follicles in the ovaries and possibly by blood tests to measure the estradiol level in the blood.

  • What about pregnancy with OHSS?

    Pregnancy is more likely in women who develop OHSS. When a pregnancy occurs in a woman who has symptoms of OHSS, the condition is likely to be aggravated and be more prolonged. For this reason, a woman who is undergoing in vitro fertilisation and who is at significant risk of developing OHSS may be advised to have all embryos frozen and stored for future use rather than replace fresh embryos and run the risk of worsening the OHSS. If a woman does become pregnant and has OHSS there is no reason why the pregnancy should be any more likely to fail.

  • Are there any ongoing concerns if I have had OHSS and become pregnant?

    To lower the risk of developing a blood clot in your legs or lungs, you will be advised to continue wearing support stockings and taking heparin (blood-thinning) injections until 12 weeks of your pregnancy.

    You may be at increased risk of developing pre-eclampsia or giving birth to your baby prematurely. However, there are no known risks to your baby’s development as a result of OHSS.

  • Can OHSS develop again in a future treatment?

    There is a tendency for this condition to recur. If one treatment has resulted in OHSS the dosage of drugs will be adjusted in any future treatment to take this into account and lessen the possibility of a recurrence. 
If you are receiving Gonadotrophin drugs for fertility treatment and develop the symptoms described above, call your infertility centre without delay.

  • Key points
    • OHSS is a potentially serious complication of fertility treatment, particularly of IVF.
    • It can range from mild to severe. Mild OHSS is common and usually gets better with time. More severe cases require specialist care and hospital admission.