Gonadotrophin therapy (FSH/LH) is a highly successful way of inducing ovulation and pregnancy for women who have anovulation associated with PCOS who have failed to conceive with anti-oestrogens.
The complications of gonadotrophin therapy are multiple pregnancies and ovarian hyperstimulation syndrome (OHSS), both almost entirely dependent on a large number of follicles that develop as a result of ovarian stimulation.
The principle of the classic chronic low dose regimen is to employ a low starting dose (maximum 75 IU) for a minimum of 14 days with no dose change and then use small incremental dose rises ( usually 25- 37.5 IU) when necessary, at intervals of not less than 7 days, until follicular development is initiated.
The purpose of this form of therapy is to achieve the development of a single dominant follicle rather than the development of many large follicles and so avoid the complications of OHSS and multiple pregnancies.
It produces a remarkably consistent rate of cycles with just one ovulation of around 70%, a pregnancy rate of 40% and an extraordinarily low prevalence of OHSS which is almost completely eliminated and a multiple pregnancy rate of 5.7%. The majority of patients (90%) on a low dose protocol develop a single large follicle with criteria for the triggering of ovulation within 14–16 days without any change in the initial dose for 14 days.