The biphasic pattern of end-expiratory carbon dioxide pressure: a method for identification of the fertile phase of the menstrual cycle.

Objective: To examine the changes of end-tidal carbon dioxide pressure (P(ET)CO(2)) during the menstrual cycle.

Design: Controlled clinical study.

Setting: Department of Gynecologic Endocrinology and Reproductive Medicine, Medical University of Innsbruck, Austria.