Proof of concept use of progesterone/estradiol ratio to investigate late follicular progesterone in women with low number of preovulatory follicles

BACKGROUND: The aim of this study was to investigate late follicular progesterone (P) serum levels in women with a low number of preovulatory follicles in the assisted reproductive technologies (ART) setting. METHODS: Fifty-five consecutive women having four or fewer preovulatory follicles of >14 mm on the day of human chorionic gonadotropin (hCG) administration were prospectively evaluated. Spearman correlation tests were performed between serum estradiol (E₂) level, serum P level, P/E₂ ratio, number of preovulatory follicles, oocytes and embryos. Women enrolled were further divided into two groups in accordance with the P/E₂ ratio on the day of hCG administration and compared. RESULTS: Serum E₂ level correlated positively with P serum level (r_s=0.36, P<0.01), number of mature follicles (r_s=0.50, P<0.01) and number of oocytes retrieved (r_s=0.36, P<0.05), whereas negatively with P/E₂ ratio (r_s=- 0.68, P<0.01). Likewise, number of preovulatory follicles correlated positively with E₂ level (r_s=0.50, P<0.01), P level (r_s=0.27, P<0.05) and number of oocytes retrieved (r_s=0.33, P<0.05), while it correlated negatively with P/E₂ ratio (r_s=-0.33, P<0.05). Furthermore, women with P/E₂ ratio >1 on the day of hCG administration received considerably higher total follicular stimulating hormone (FSH) dosage and achieved significantly lower number of oocytes and embryos as compared to controls. CONCLUSIONS: The reverse relationship between number of preovulatory follicles and P/E₂ ratio implies that P rise is not only the result of increased steroidogenic activity, but other oocyte-follicle disrupted mechanisms seem to be involved. An exaggerated FSH stimulation appears to disrupt further these mechanisms.