Proportion of menstrual cycles that are ovulatory differs from the proportion that are regular during the early post-menarcheal years

Comparison of the percent of menstrual cycles that are 21 to 45 days duration (grey) and percent of menstrual cycles that are ovulatory (orange) by post-menarcheal age through young adulthood. Ovulation was determined by normalcy of urinary pregnanediol glucuronide in weekly samples collected during the last 12 days of each menstrual cycle; cycles with clearly detectable but subnormal pregnanediol are here designated as having luteal insufficiency (blue). Pregnanediol is a metabolite of the progesterone secreted by the corpus luteum formed in response to ovulation. Pregnanediol concentrations indicating antecedent attenuated ovulation signify that most of the menstrual cycles that are not ovulatory had sufficient cyclic follicular activity to generate an immature corpus luteum, rather than being truly anovulatory.