To add or not to add LH: comments on recent commentaries.

Human reproductive evolution, involving a complex interaction of the hypothalamic-pituitary-ovarian axis, the release of pulsatile and threshold concentrations of gonadotrophins and positive and negative feedback systems, has ensured the release of a single viable egg and functioning corpora lutea in the natural menstrual cycle. The use of follicular stimulation regimens to obtain multiple eggs has resulted in a compromise - in terms of the risk of ovarian hyperstimulation, cost, multiple pregnancies, wastage of or the need for cryopreservation of surplus embryos. Even some women with apparently normal menstrual cycles might become 'poor responders' when administered with follicular stimulants, and we still do not know if the incidence of oocyte aneuploidy is artificially raised after stimulation. After the advent of recombinant FSH and LH, the precise roles of these hormones individually needs to be elucidated to understand the physiological requirements for successful ovarian stimulation in each woman undergoing IVF, to maximize her chance and minimise attendant risks. One of the key debates is the role of LH, which in the natural cycle is significant, but may be redundant during ovarian stimulation for IVF. Current outcome indicators are crude when attempting to understand the physiology, and more basic research and randomized, focused clinical trials are needed.