Abstract

Progesterone is essential for endometrial receptivity, implantation and the maintenance of an early pregnancy. In spontaneous conception cycles, progesterone is produced by the corpus luteum; however, after hormonal stimulation for preparation for in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) the luteal phase is characterized by a variably severe luteal phase insufficiency. The necessity for a luteal phase support is indisputable and has to be selected according to the preceding treatment. So far, “minimal” and “optimal” ranges of progesterone levels to achieve and maintain a pregnancy are not clearly defined, neither for transfer cycles with fresh embryos nor for transfer cycles with frozen embryos.