Ovarian hyperstimulation

When we think about the risks associated with IVF, we tend to either worry about the possibility of long-term health risks or more often about the risk of the treatment not working. In fact, one of the most serious, and not uncommon, risks of IVF is ovarian hyperstimulation, often known as OHSS.

Stimulating the ovaries to produce lots of eggs is not a natural process, and hyperstimulation is not something that can occur naturally but is a direct result of fertility treatment. Some women are more at risk of OHSS than others, and the team treating you will be keep a particularly close eye out for this if you have polycystic ovary syndrome, if you are underweight or if your have had OHSS in the past. Hyperstimulation can occur during treatment or after successful treatment when the rising hormone levels in early pregnancy can have an effect, which is why women who are pregnant with twins are at greater risk.

When the ovaries are hyperstimulated they become enlarged and the balance of fluids in the body is affected. Fluid can start to gather in the abdominal cavity and this can lead to swelling, dehydration and bloating. Fluid may collect in the lungs too, and the condition can also lead to an increased risk of blood clots. Although OHSS is often mild, the condition can be very dangerous.

Clinics can usually spot women who are at risk of hyperstimulating when they carry out the regular scans during treatment as there will be large numbers of follicles developing. Blood tests can confirm that a woman is at risk. Symptoms of OHSS can include discomfort and swelling in the abdomen, nausea, reduced urine output, dehydration and breathlessness. The first thing that women notice is often a swollen stomach, and the swelling can seem to increase very rapidly.

Ovarian hyperstimulation is thought to occur in about 5% of women having IVF treatment. Although the condition is often mild, it is always important to get medical advice immediately if you suspect you may have OHSS as it can be dangerous. If you are in the middle of a treatment cycle, you may be advised to "coast" for a few days without taking more stimulating drugs to see what happens. If you are close to egg collection, the embryos may be collected and frozen so that they can be replaced safely later.