Treatments and investigations

Ovarian Hyperstimulation Syndrome (OHSS)


When the ovaries are stimulated to produce eggs, the response can at times be excessive. During Ovulation Induction (see Ovulation Induction information) and Intrauterine Insemination treatment (see Intrauterine Insemination information) cycles, you may develop lower abdominal discomfort due to enlarged ovaries. However it is very unusual to develop more than mild symptoms as only 1 ? 2 egg follicles are being stimulated.

In IVF treatment, the response to stimulation with gonadotrophin drugs can occasionally be very excessive. There is then a significant risk of developing a potentially serious complication called Ovarian Hyperstimulation Syndrome (OHSS). The women who are most likely to develop OHSS are those with polycystic ovary syndrome (PCOS).

In IVF treatment, 5% of women will develop moderate symptoms of OHSS (see below). Severe OHSS occurs in less than half of 1% of all IVF procedures.

During your treatment, the serial scanning of your ovaries means that the clinic staff will be aware if you are growing a greater than average number of egg follicles and therefore at risk of OHSS.  At the time of the final scan your clinic will have made a fairly accurate estimate of the number of eggs that are likely to be collected if egg retrieval goes ahead. The risk of severe OHSS increases significantly if you are already experiencing discomfort from very enlarged ovaries, if your ovaries contain a very large number of mature egg follicles and if you have a rapidly rising oestradiol hormone blood level. Although it will be disappointing to you, your treatment cycle will be abandoned.

When treatment is abandoned before the final egg maturing injection of human chorionic gonadotrophin (hCG) is administered (see IVF information), the ovaries rapidly shrink back to their normal size.

OHSS can only develop after hCG has been given. This usually becomes apparent during the week following egg retrieval. Even when the response has been very satisfactory it is still possible to develop mild / moderate OHSS. The enlarged ovaries can cause pain, abdominal distension, nausea, vomiting and diarrhoea. It is often best to admit you for observation and monitoring. It is then possible to convert a moderate form of OHSS into a mild form of the condition. This will involve carrying out blood tests once or twice daily, maintaining fluid intake with an intravenous drip and keeping a careful check on urine output. Simple pain killers are adequate in controlling the discomfort of enlarged ovaries. If a pregnancy does not result, a period follows, the very enlarged ovaries return to normal size and the OHSS signs and symptoms resolve and disappear.

If a pregnancy does result after embryo transfer, there is an outpouring of hCG and the OHSS symptoms worsen dramatically. Clinics are very anxious to avoid this complication.

Occasionally surprises occur when many more eggs are collected than expected. In this situation all suitable embryos are cryopreserved (frozen) and stored for your future use (see Cryopreservation (freezing) of Embryos and Frozen Embryo Transfer (FET) information) so as to avoid the severe form of OHSS that can occur when a pregnancy results.

In severe cases of OHSS, water can collect in the abdomen causing considerable discomfort and occasionally in the chest where it can cause difficulty in breathing. This water comes from the blood. As a result of this water loss, blood cells become sludgier and may have a greater tendency to clot. The loss of water from the blood means that the kidneys may slow down their production of urine and this must be carefully monitored. It may be necessary to give you blood-thinning injections to prevent a deep vein thrombosis, and transfusion of intravenous fluids to reduce the collection of fluid in the abdomen and encourage the production of urine. Very occasionally, a large fluid collection from the abdomen has to be drawn off to improve comfort. It is very rare that fluid in the chest (pleural effusion) has to be drained.

Rarely the most severe form of OHSS may be life threatening,

If you are at home after embryo transfer and your abdomen becomes bloated, nausea develops, or you become breathless, or you notice that you are not passing much urine, ring your clinic. You are never wasting their time. In the meantime drink copious amounts of water to encourage the kidneys to produce urine. Do not decline arrangements to admit you as an emergency. This is not a situation where you can afford to play games!

Clinics will provide you with information of what you should do in an emergency. Make sure that you have the emergency telephone number. Make sure that a member of the clinic staff can always be contacted.

If you should feel unwell particularly during the two weeks after egg retrieval, it is essential that you inform your clinic at any time night or day.

March 2009