Introduction: Hypothalamic-pituitary axis maturity has been believed to be the rate-limiting step in the development of ovulatory menstrual cycles. We hypothesized that, given current nutritional conditions, hypothalamic-pituitary axis maturation would be relatively rapid in menarcheal girls.

Methods: Daily urine and menstrual records were collected for two years each from 10 girls aged 11 to 13 at study entry. Urinary excretion of LH, FSH, estradiol (E1c) and progesterone (Pdg) metabolites were measured using established ELISAs. An objective algorithm detected rises of LH, FSH, E1c and Pdg consistent with follicular maturation and/or ovulation.

Results: Nine of 10 ten girls enrolled into the study experienced the onset of menarche prior to or during the 2 year collection period. LH and FSH surges, as well as small amplitude Pdg increments, were observed prior to menarche. Regular, ovulatory-appearing cycles with LH surges and gradually increasing and more sustained Pdg rises were observed over time after menarche, although duration of Pdg elevations remained shorter than in adult women (8.9 ± 1.0 versus 12.1 ±0.8 days, p=0.043). E1c levels leading to LH/FSH surges were lower in perimenarcheal girls than adult controls, and bleeding episodes did not uniformly correlate with hormone patterns. Progressive increases in FSH and Pdg, but not LH or E1c, were observed in association with menarche.

Conclusion: Mature hormone patterns are established within several months of and even prior to menarche in normal weight perimenarcheal girls. Factors determining menstrual bleeding in perimenarcheal girls may not be solely dependent upon reproductive hormones or the neuroendocrine axis.