Changes in the ovarian follicle, endometrial thickness, and serum hormone levels during a 28-day menstrual cycle. P, progesterone; E2, estradiol; LH, luteinizing hormone; FSH, follicle-stimulating hormone. (Used with permission from Hoffman BL, et al. Chapter 15. Reproductive endocrinology. In: Hoffman BL, et al., eds. Williams Gynecology. 2nd ed. New York, NY: McGraw-Hill; 2012) Source: Reproductive Endocrinology and Infertility, The Johns Hopkins Handbook of Obstetrics and Gynecology Citation: Szymanski LM, Bienstock JL. The Johns Hopkins Handbook of Obstetrics and Gynecology; 2015 Available at: http://obgyn.mhmedical.com/DownloadImage.aspx?image=/data/books/1657/szymanski_ch04_fig-04-01.png&sec=107291313&BookID=1657&ChapterSecID=107291310&imagename= Accessed: October 31, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved