Some women experience mild unpleasant symptoms, but these are normally short-lived and are no cause for concern. They may include hot flushes, feelings of depression and irritability, headaches and restlessness at night.

Despite careful monitoring, a small number of women may develop a mild or moderate form of over-response to the drugs, and too many eggs may develop. In some cases cysts may appear on the ovaries and fluid may collect in the abdominal cavity, causing discomfort. The condition should be monitored by a fertility specialist, and can be treated by bedrest, drinking plenty of fluids and taking simple painkillers. The cycle may have to be abandoned.

Very rarely, in about 1% of cases, a more serious reaction to the drugs causes a very large number of eggs to develop and the ovaries to swell. This is known as ovarian hyperstimulation syndrome (OHSS). Symptoms such as nausea and vomiting, abdominal pain and swelling, and shortness of breath may occur. A patient may also feel weak and faint and notice a reduction in urine output. These complications require urgent hospital admission to restore the fluid balance and monitor progress. Patients should ask clinics for information about their policy for avoiding OHSS and also the signs for which patients should look.