Endometrial dating and determination of the window of implantation in healthy fertile women

Objective: To reassess endometrial morphological criteria of normality identifying the best morphological and molecular “implantation window” indicators in normal women. Design: Prospective clinical study. Setting: Assisted reproductive unit. Patient(s): Fourteen healthy volunteers. Intervention(s): Blood sampling for LH, E 2, and progesterone (P4) determinations. Daily vaginal ultrasounds. Two endometrial biopsies per volunteer, 7 days apart, during luteal phase. Main Outcome Measure(s): Endometrial dating, pinopodes formation, immunohistochemical determination of integrins (αvβ3, α4β1), leukemia inhibitory factor (LIF), interleukin-1 receptor type I (IL-1R tI), mouse ascites Golgi (MAG), the transmembrane mucin (MUC-1), and P4 receptor expression. Result(s): In 26 of 28 biopsies observers agreed; in two biopsies there was a discrepancy (difference of 72 hours). With use of LH peak, 24 of 26 samples were in phase, and 2 were 3 days behind. Pinopodes appeared on days 20–21 and persisted through day 28 in small groups or larger areas. β3 Integrin was highly expressed in luminal and glandular epithelium from day 22 through 28; 48 hours thereafter pinopodes appeared. α4 Subunit exhibited luminal epithelium reaction positivity on days 22–23 and glands on days 18–23. LIF and IL-1R tI showed weak, erratic expression. MAG antibodies showed luminal epithelium expression up to day 22 and glands up to day 25. MUC-1 showed positivity during the whole luteal phase. P4 receptors were positive through day 20 and at the end of the luteal phase. Conclusion(s): The three most cited markers that frame the window of implantation do not correlate in our material. Pinopodes are present from day 20 on; β3 and α4 integrin subunits indicate a window opening on days 22–23.