Determination of endometrial prolactin in vivo as a marker for endometrial development in spontaneous ovulatory cycles and in vitro fertilization cycles.

Decidual prolactin was directly determined in endometrial tissue in order to assess its potential role in improving the accuracy of the diagnosis of luteal-phase defect (LPD). Endometrial biopsies of 124 women with regular cycles (group 1) and 13 women with controlled ovarian hyperstimulation and progesterone-supported cycles (group 2) were evaluated in the secretory phase. In addition, decidual prolactin was measured in the luteal phase of the in vitro fertilization (IVF) cycles. The biopsies dated on or after day 25 showed a significant increase in the slope of the regression line of the cycle day versus decidual prolactin content (p < 0.05). Delayed endometrium was not characterized by a lower amount of decidual prolactin compared with biopsies with the same histological dating. On day 27 of the cycle, less prolactin was measured in the out-of-phase biopsies (p < 0.05). A large inter-individual variation in endometrial prolactin tissue content was noticed. In group 2 all biopsies but one were in phase. Compared to the in-phase biopsies of group 1, a significantly higher amount of prolactin was found in group 2. Production of endometrial prolactin in vivo is associated with decidualization of the stromal cells. However, because of the large inter-individual variation, determination of prolactin is not of adjuvant diagnostic value for clinical assessment of LPD. Three factors might explain the higher amount of decidual prolactin in group 2 compared to group 1: (1) a higher serum progesterone concentration owing to an increased production by multiple corpora lutea, or because of the administered progesterone; (2) increased estradiol levels and thus progesterone receptors; and (3) direct stimulation of decidualization by gonadotropins.