Basal serum level of Δ4-androstenedione reflects the ovaries' ability to respond to stimulation in IVF cycles: setting up a new reliable index of both ovarian reserve and response.

Baseline serum Δ4-A, presumably crucial for ensuring a regular follicular growth, is a reliable marker of ovarian response to stimulation. Since the ovarian capacity to respond to gonadotropins does not depend exclusively on the presence of follicles, we suggest a new index, the G-index, able to contemplate both the ovarian reserve and the Δ4-A level.