Sun BZ, et al. - In 23 early post-menarchal girls (gynecologic age 0.4-3.5 yrs), researchers determined the association between progesterone (P4) exposure, sleep-related slowing of LH pulses in the follicular phase (FP), and the inter-cycle FSH rise, which promotes folliculogenesis. For this investigation, study participants underwent hormone measurements and pelvic ultrasounds during two consecutive cycles and one frequent blood sampling study with concurrent polysomnography during the FP. In late puberty, rising P4 levels due to follicle luteinization and ovulation can lead to a slower LH pulse frequency during sleep in the FP. However, a normal increase in FSH and follicle growth can occur in the absence of P4-associated slowing. Therefore, these investigations indicate that an immature LH secretory pattern during sleep is unlikely to contribute to menstrual irregularity in the early pos-menarchal years.