English: This diagram shows the percentage increases in both estradiol and progesterone serum levels across the menstrual cycle. Both hormone levels rise from their low levels during menstruation (early follicular phase). It is based on the original study published here: Nielsen HK, Brixen K, Bouillon R, et al. Changes in biochemical markers of osteoblastic activity during the menstrual cycle. Journal of Clinical Endocrinology and Metabolism 1990;70:1431-37. This image was originally published in: Prior JC. Women’s Reproductive System as Balanced Estradiol and Progesterone Actions—a revolutionary, paradigm-shifting concept in women’s health. Drug Discovery Today: Disease Models 2020;32:31-40; http://DOI.org/10.1016/j.ddmod.2020.11.005. Note that the journal article is licensed CC BY-NC-ND 4.0, but this particular image is licensed CC BY-NC-ND 4.0.