Fig. 5. Simultaneous luteinizing hormone and progesterone secretion patterns in the late luteal cycle phase in a normal woman. Secretory events that were identified as pulses are indicated by asterisks for luteinizing hormone and progesterone. In the mid to late luteal phases of the cycle, there is synchrony between luteinizing hormone and progesterone secretion. (Soules MR, Clifton DK, Steiner RA, et al: The corpus luteum: Determinants of progesterone secretion in the normal menstrual cycle. Obstet Gynecol 71:659, 1988.)