Received December 28, 1997
Accepted January 16, 1999

Introduction: The pregnancy rate as well as the implantation rate in assisted reproduction have remained relatively constant in spite of studies and progress made during the last years. An embryo capable of implanting and a receptive endometrium are needed in order to achieve pregnancy. Several aspects of progesterone such as different routes of administration in the luteal phase for assisted reproduction are expanded in the present paper. In CEGyR a prospective randomized study was done to compare assisted reproductice results with two different routes of progesterone intramuscular vs intravaginal. Material and Methods: Since November 1994 to May 1995 one hundred patients were randomize in two groups. Group I (n=50) received 100 mg daily of intramuscular progesterone (Proluton NR) and group II (n=50) received 800 mg daily of micronized progesterone intravaginally. Results: No significant differences were observed in patient's age, number and quality of aspirated oocytes, fertilization rate. Plasma progesterone leveis were higher on day +3 in the group that received intramuscular progesterone. The pregnancy rate was similar in both groups. Conclusion : Progesterone administered intravaginally remained in physiologic leveis in the luteal phase. Since intravaginally progesterone administration is more comfortable for the patient this route seems to be preferable.