It is not yet established whether or not treatment with gonadotrophins increases the baseline risk of these tumours in infertile women. • Women with generally recognised risk factors for thrombosis, such as a personal or family history, severe obesity (Body Mass Index > 30 kg/ m2) or thrombophilia, may have an increased risk of venous or arterial thrombo-embolic events, during or following treatment with gonadotrophins.