During ovarian stimulation, administration of GnRH analogues maintains a suppression of endogenous hormone levels. In 5-30% of cases there is a premature increase of progesterone on the day of hCG administration (the last injection of the program).

Several studies have shown that the increase of progesterone above 1 ng/ml is associated with reduced pregnancy rates, while other studies have failed to show such an effect. The mechanism through which pregnancy rates may be affected has not been elucidated yet, but is seems that increased progesterone has a negative impact on the quality of the endometrium.

In view of the contradicting data in the literature, it is important to conduct more prospective randomized controlled trials in a large number of patients, in order to clarify the role of progesterone increase on pregnancy rates.