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 (rs=0.36, P<0.01), number of mature follicles (rs=0.50, P<0.01) and number of oocytes retrieved (rs=0.36, P<0.05), whereas negatively with P/E2 ratio (rs=- 0.68, P<0.01). Likewise, number of preovulatory follicles correlated positively with E2 level (rs=0.50, P<0.01), P level (rs=0.27, P<0.05) and number of oocytes retrieved (rs=0.33, P<0.05), while it correlated negatively with P/E2 ratio (rs=-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.