The relationship between gonadotrophic hormones and progesterone in the mid-luteal phase

It is known that progesterone (PRG) exerts a negative feedback on gonadotrophic hormones in the mid-luteal phase. However, we are unaware of any data in the literature that states the nature of this relationship, for example, is it linear or not?

To determine the relationship between gonadotrophic hormones and PRG in the mid-luteal phase using routine clinical assays and routine clinical patient data.

Retrospective mid-luteal phase serum follicle-stimulating hormone (FSH), leutinizing hormone (LH) and PRG data from 393 women were obtained from the laboratory computer system. Polynomial regression analysis was performed using this data to get the best fit curves. Using the best fit curve, the lowest PRG concentration on the linear phase of the best fit lines were determined with the corresponding gonadotrophic hormone concentrations.

The expected inverse relationships were observed. However, polynomial regression curves provided better data fits than linear regression for both LH and FSH. A scatter about the best fit curves was noted for both FSH and LH with the data for LH having a grater scatter around the curve than FSH. The lowest PRG concentration on the linear phase of the best fit curves were 53 and 45 nmol/l for the LH and FSH curves respectively. The LH and FSH concentrations in the linear phase were 4.78 and 3.10 micro/l respectively.

Our data shows that the relationships between LH or FSH and PRG are curvi-linear. Beyond PRG concentrations of 60 and 44 U/l, there is no further decrease in the LH and FSH concentrations respectively. These cut-offs could be physiologically significant. However, due to the large scatter around the curve, significant differences in FSH and LH concentrations may be found when such PRG concentrations are present and may include low concentrations.