Women with consistently or variably elevated early follicular phase FSH.

Sir, We thank Drs El Hakim and Cahil for their interest and reaction to our paper (de Koning et al. 2008). It is true that the highest measured FSH level is the one that makes clinicians aware of the possible low ovarian reserve. It is known that a normal or moderately elevated FSH can still be found in women with low ovarian reserve due to variable FSH levels and possibly variable cohort size. In our paper, we categorize the women with elevated FSH levels as ‘High, High’ (H,H group) when they showed an elevated FSH level both in a screening cycle and in the study and as ‘High, Low’ (H,L group) when they showed high FSH levels in a screening cycle but normal (,10 IU/l) in the study cycle. The answer to the question whether the women moved between the groups is as follows: of the 11 women in the original H,H group, five had a normal FSH level in the third cycle and of the 11 women in the original H,L group, six had an elevated FSH level in the third cycle. This indeed shows the strong inter individual variation of FSH in these women. And interestingly, this is associated with concomitantly large variation in inhibin B levels in the preceding luteal phase, and in our view, this could be a useful value to evaluate in the cycle immediately before the stimulation for IVF. The anti-Müllerian hormone (AMH) levels were indeed not different in the patient groups with either normal or elevated Day 3 FSH values and this is in line with observations that AMH does not vary much between the cycles (Fanchin et al., 2005) and is not under a stringent extra ovarian control (La Marca et al., 2006). Our study was not designed to correlate FSH levels or AMH levels or AFC to clinical pregnancy rates but to describe the endocrinology in the spontaneous cycle of women with elevated FSH levels in the early follicular phase. In a prospective study, these parameters can be studied in this respect.