Contribution of preovulatory-phase small follicles to the ovarian response in stimulated cycles.

The usual criteria for ovulation induction in stimulated cycles take into account the number of follicles greater than 14-16 mm in diameter. We have retrospectively investigated how the presence of small (8-12 mm) follicles at the time of the last scan influences the ovarian response for in-vitro fertilization (IVF). The mean number of small follicles was nearly constant (3.8 to 5.9) and did not correlate with the number of large (greater than 12 mm) follicles in various protocols for ovarian stimulation. In patients stimulated under the influence of a gonadotrophin releasing hormone (GnRH) agonist, the number of small follicles was correlated with the oestradiol (E2) peak level and with the number of recovered oocytes. Our data demonstrate a significant contribution of follicles less than or equal to 12 mm to peripheral E2 levels and oocyte production for IVF.