A prospective randomized comparison of intramuscular or intravaginal natural progesterone as a luteal phase and early pregnancy supplement.

A luteal phase defect has been demonstrated in cycles stimulated using a protocol including a gonadotrophin releasing hormone agonist (GnRHa). We have conducted a randomized prospective study of luteal and early pregnancy supplementation in 262 women selected for in-vitro fertilization (IVF), gamete intra-Fallopian transfer (GIFT) or zygote intra-Fallopian transfer (ZIFT). Either intramuscular progesterone in oil (50 mg/day) or intravaginal micronized progesterone (600 mg/day) was used as luteal supplement. In association with oestradiol valerate, progesterone administration was initiated from the day before oocyte retrieval until the 12th week of pregnancy. The implantation rate just failed to reach statistical significance (P = 0.07) in favour of the group receiving intravaginal progesterone. In the latter group, we observed a higher clinical pregnancy rate (33.6 versus 26.7%, not significant). Despite lower plasma progesterone levels, a lower first trimester abortion rate (P less than 0.05) was found in the intravaginally treated group. Intravaginal micronized progesterone was well tolerated by all patients and appeared more effective than intramuscular progesterone in improving the implantation rate, and in decreasing the incidence of abortions in stimulated cycles including GnRHa.