Endocrine pathophysiology of luteal phase deficiency as assessed by GnRH/TRH stimulation tests performed in the early follicular and midluteal phases of the menstrual cycle.

To investigate endocrine pathophysiology of luteal phase deficiency (LPD), GnRH/TRH stimulation tests were performed in the early follicular (EFP) and midluteal phases (MLP) of the menstrual cycle in 52 infertile women with a history of short luteal phase, in whom pituitary responsiveness to GnRH/TRH and steroidogenic competency of the corpus luteum were analyzed. Twelve women with either elevated basal-LH or exaggerated PRL response to GnRH/TRH in EFP were eliminated, and the remaining 40 women were studied. Basal-FSH in EFP inversely correlated with steroidogenic parameters in MLP, indicating that compromised folliculogenesis causes LPD. In a fraction of LPD women, decreased basal-LH in MLP was associated with decreased basal-progesterone (p), in spite of normal steroidogenic potential of the corpus luteum, suggesting that aberrant LH secretion is another progenitor of LPD. The other group of LPD women showed shortening of high phase period and/or extravagant discrepancy in endometrial dating without apparent abnormal endocrine parameters, suggesting that unknown factors are involved in establishment of LPD. From the diagnostic point of view, they were discriminated into three groups, normal, incomplete LPD and complete LPD groups, with a modified classification of LPD; 1) shortening of high phase period < 11 days, 2) delay in histological to chronological dating of the endometrium > 2 days, and 3) decreased max-P in MLP < 10 ng/ml. Normal (n = 14) and complete LPD (n = 7) groups consisted of women having all the criteria of classification within and out of the cut-off values, respectively. The remainders were enrolled into incomplete LPD group (n = 19). Complete LPD group mainly consisted of women having compromised folliculogenesis as a cause of LPD. In contrast, incomplete LPD group appeared a mixture of heterogeneous populations as to the genesis of LPD. GnRH/TSH stimulation test, especially when performed in MLP, would unveil endocrine pathophysiology of LPD and provide an accurate standard for diagnosis of LPD.