Figure 9From: A critical period of progesterone withdrawal precedes menstruation in macaquesThe Luteal-Follicular Transition. This diagram illustrates the various phases that follow P withdrawal in the primate endometrium, beginning with Premenstrual Regression, Menstrual Sloughing, Suface Repair, etc. The critical period is shown as a 2 day period during which menses-inducing factors build up to a threshold of inevitability.Back to article page