Luteal phase support in ART treatments.

In a normal spontaneous menstrual cycle, the luteal phase is characterized by the production and secretion of estradiol (E) and progesterone (P) from the corpus luteum (CL) in an episodic manner. The steroidogenesis of the CL is dependent on continued tonic luteinizing hormone (LH) secretion (Fritz and Speroff, Clinical gynecologic endocrinology and infertility, 8th edn. Wolters Kluwer, Lippincott Williams & Wilkins, Philadelphia, 2011). The dependence of the CL was further supported by the prompt luteolysis that followed the administration of GnRH analogues or withdrawal of GnRH when ovulation has been induced by the administration of pulsatile GnRH (Hutchison and Zeleznik, Endocrinology 115:1780-1786, 1984; Fraser et al., Hum Reprod 12:430-435, 1997). Progesterone concentrations normally rise sharply after ovulation, reaching a peak approximately 8 days after the LH surge. Since the secretion of E and P during the luteal phase is episodic and correlates closely with LH pulses, relatively low mid-luteal progesterone levels can be found in the course of a totally normal luteal phase (Fritz and Speroff, Clinical gynecologic endocrinology and infertility, 8th edn. Wolters Kluwer, Lippincott Williams & Wilkins, Philadelphia, 2011).