The human chorionic gonadotrophin (HCG) trigger used for final follicular maturation in connection with assisted reproduction treatment combines ovulation induction and early luteal-phase stimulation of the corpora lutea. The use of a gonadotrophin-releasing hormone agonist (GnRHa) for final follicular maturation has, however, for the first time allowed a separation of the ovulatory signal from the early luteal-phase support. This has generated new information that may improve the currently employed luteal-phase support. Thus, combined results from a number of randomized controlled trials using the GnRHa trigger suggest an association between the reproductive outcome after IVF treatment and the mid-luteal-phase serum progesterone concentration. It appears that a minimum mid-luteal progesterone threshold of approximately 80-100 nmol/l exists, which, when surpassed, results in reduced early pregnancy loss and an increased live birth rate. Further, the trade off between the HCG bolus and the subsequent risk of ovarian hyperstimulation syndrome has resulted in a trend to reduce the HCG bolus from 10,000 IU to 6500-5000 IU, which augments the HCG/LH deficiency during the early/mid-luteal phase. The mid-luteal HCG/LH shortage results in an altered progesterone profile, showing the highest concentration during the early luteal phase, contrasting with the mid-luteal peak seen in the natural menstrual cycle.