Although reproductive aging has been separately related to elevated FSH and shorter follicular phase (FP), the direct association between both parameters has not been investigated. Also, the exact effects of increased FSH on estrogen production are yet to be established.
A large database of daily urinary concentrations of FSH, LH, and estrone 3-glucuronide (E1G) from 37 regularly menstruating women (median 11 cycles per patient) was used. Initial FSH levels (iFSH) were estimated as the mean value of d 1-5. The day of E1G take-off (ETO) was determined by an algorithm, and accordingly, the FP was divided into early (d 1 to ETO) and late (ETO+1 to LH peak). FP maximum and integrated E1G were calculated.
Subjects were distributed according to their mean iFSH into three categories (≤5, >5 to 10, and >10 IU/liter). There was a gradual decrease in FP length with increasing category (15.2 ± 3.8, 14.1 ± 3.6, and 13 ± 2.6 d, respectively; P < 0.0001). A similar effect occurred in early FP (7.5 ± 4, 6.4 ± 3.7, and 5.4 ± 2.7; P < 0.0001); in contrast, late FP was unaffected (7.7 ± 2.1, 7.7 ± 2.1, and 7.6 ± 2.4; P = 0.86). No consistent increase in E1G was found with advancing iFSH category; however, women with mean initial LH higher than 6 IU/liter had significantly elevated maximum (P < 0.0001) and integrated (P = 0.002) E1G.
FP length decreases in parallel with increasing iFSH, with a selective effect on the early FP. Increased FSH does not affect E1G; however, elevated initial LH level was related to higher E1G.