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 gonadotrophinsmay result in blockage of the endogenous luteinizing hormone(LH) surge, but the reasons for this are not known. Ten normallyovulating women with longstanding infertility volunteered forthis study. They were treated with 225 IU follicle-stimulatinghormone (FSH) daily s.c. in a pulsatile manner (28 IU every3 h) starting on cycle day 2. Serum FSH and oestradiol levelsincreased and serum LH levels decreased significantly duringthe 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 significantlylower and the number of follicles 12–15 mm in diameterand their total fluid volume was significantly greater in thecycles without an endogenous LH surge. Basal LH levels in thecycles without an LH surge increased soon after the end of theFSH treatment (cycle day 18), while FSH levels were still verylow without any incremental tendency. These results suggestthat a high number of small follicles may have a suppressiveeffect on both tonic and mid-cycle gonadotrophin secretion.Furthermore, the LH suppressive mechanism seems to be differentfrom that of the FSH.