Based on the data obtained from a phase III, multicenter, open-label, randomized clinical trial that compared the use of GnRH agonist vs. antagonist for LH-suppression in IVF cycles, the present study attempted to determine the effect of LH level on steroid concentrations and IVF outcomes in the GnRH antagonist protocol.

A total of 109 patients with the GnRH antagonist protocol were stratified into three subgroups according to the stimulation day six LH levels (LH <25%, 25–75%, and >75%), and the effect of LH on steroid biosynthesis and the related IVF outcomes between subgroups was observed.

In comparing the three subgroups of GnRH antagonist, no difference in number of oocytes, top quality embryos and ongoing pregnancy was observed. The high LH group on day six was exposed to significantly lower concentrations of rFSH from day six onwards, and had significantly higher estradiol levels on the day of hCG. The progesterone levels did not differ between groups at the start of the stimulation, but patients with the highest LH on day six also had significantly (P < 0.0001) higher progesterone levels on day six (higher estradiol on day six and hCG, lower total rFSH dosage). Due to the significantly lower increase in progesterone in the high LH group between day six and the day of hCG, no difference in progesterone level was observed on the day of hCG.

For steroid biosynthesis, early follicular phase LH levels help pregnenolone metabolize primarily via the ∆5 pathway in the GnRH antagonist stimulation protocol, but not via the ∆4 pathway.