Part of “CHAPTER 95 – THE NORMAL MENSTRUAL CYCLE AND THE CONTROL OF OVULATION“

In normal ovulatory cycles, the mean interval from the late follicular phase peak estrogen level to the peak LH level is ˜24 hours. Ovulation follows ˜9 hours later, for a total interval of ˜33 hours.104 In in vitro fertilization protocols with human menopausal gonadotropin-induced ovarian stimulation and human chorionic gonadotropin (hCG) supplementation, follicular rupture seldom occurs until 36 hours after hCG administration (mimicking the endogenous LH surge). Similarly, initial ovulation seldom occurs until 34 or more hours after treatment with clomiphene citrate and hCG.

The actual events that lead to expulsion of the oocyte and that occur after either the natural or the induced LH surge are incompletely understood. It is not surprising that many of the biochemical and biophysical processes surrounding ovulation can be mimicked in vitro by cyclic adenosine monophosphate, in view of the fact that gonadotropins act by binding to receptors that are linked to cyclic adenosine monophosphate (see Chap. 94).