Comparison between different routes of progesterone administration as luteal phase support in infertility treatments

Different routes of natural progesterone supplementation have been tried as luteal phase support in infertility treatments, Orally administered proges terone is rapidly metabolized in the gastrointestinal tract and its use has proved to be inferior to i.m. and vaginal routes. Progesterone i.m. achiev es serum progesterone values that are within the range of luteal phase and results in sufficient secretory transformation of the endometrium and satis factory pregnancy rates. The comparison between i.m. and vaginal progestero ne has led to controversial results as regards the superiority of one or th e other in inducing secretory endometrial transformation. However, there is increasing evidence in the literature to favour the use of vaginal progest erone. Vaginally administered progesterone achieves adequate endometrial se cretory transformation but its pharmacokinetic properties are greatly depen dent on the formulation used. After vaginal progesterone application, discr epancies have been detected between serum progesterone values and histologi cal endometrial features. Vaginally administered progesterone results in ad equate secretory endometrial transformation, despite serum progesterone val ues lower than those observed after i.m. administration, even if they are l ower than those observed during the luteal phase of the natural cycle. This discrepancy is indicative of the first uterine pass effect and therefore o f a better bioavailability of progesterone in the uterus, with minimal syst ematic undesirable effects.