Objective: To assess effects of biopsy timing and fertility status on inter- and intraobserver variability in dating of the endometrium.
Design: Endometrial biopsy slides randomly selected from a multicenter study testing the utility of biopsy in the diagnosis of infertility were distributed to three gynecologic pathologists, who estimated cycle day using standard criteria. Readers were blinded to the purpose of the study, patient age, fertility status, or timing of biopsy relative to LH surge or next menses.
Setting: Multicenter academic research programs in reproductive medicine.
Patient(s): Eighty-two women with proven fertility, 83 infertile patients.
Intervention(s): Endometrial biopsy during midluteal (days 21-22) or late (days 26-27) luteal phase.
Main outcome measure(s): Intraclass correlation coefficient (ICC), kappa.
Result(s): Overall agreement was excellent (ICC 0.88); addition of readings by local pathologists decreased ICC only slightly. In subgroup analyses, ICCs were lowest for infertile women during the midluteal phase (0.65 vs. 0.71 for fertile women in the midluteal phase, and 0.88-0.90 for both groups in the late luteal phase). Intraobserver reliability was excellent (0.9-0.99). Agreement for diagnoses of "out-of-phase" was only moderate, with kappa values between 0.4 and 0.6.
Conclusion(s): Observer variability in dating the endometrium was greatest in infertile women during the window of implantation.