Endocrine and follicle characteristics of cycles with and without endogenous luteinizing hormone surges during superovulation induction with pulsatile follicle-stimulating hormone.

The induction of superovulation in women with human gonadotrophins may result in blockage of the endogenous luteinizing hormone (LH) surge, but the reasons for this are not known. Ten normally ovulating women with longstanding infertility volunteered for this study. They were treated with 225 IU follicle-stimulating hormone (FSH) daily s.c. in a pulsatile manner (28 IU every 3 h) starting on cycle day 2. Serum FSH and oestradiol levels increased and serum LH levels decreased significantly during the FSH treatment, as compared to their spontaneous cycles. Only five women displayed an LH surge during the FSH treatment. Serum FSH and LH levels during treatment were significantly lower and the number of follicles 12-15 mm in diameter and their total fluid volume was significantly greater in the cycles without an endogenous LH surge. Basal LH levels in the cycles without an LH surge increased soon after the end of the FSH treatment (cycle day 18), while FSH levels were still very low without any incremental tendency. These results suggest that a high number of small follicles may have a suppressive effect on both tonic and mid-cycle gonadotrophin secretion. Furthermore, the LH suppressive mechanism seems to be different from that of the FSH.