Objective: To investigate endometrial dating during the conception cycle.
Design: Endometrial biopsies of the last half of the luteal phase of conception cycles were dated based on urinary luteinizing hormone (LH) surges.
Setting: Endometrial samples were obtained from women attending the fertility clinic of the Department of Obstetrics and Gynecology at Gunma University Hospital.
Patients: One hundred eighty-five women, of whom 15 (8.1%) conceived during this study.
Main outcome measures: Urinary LH surge, serum progesterone (P) levels, and endometrial dating.
Results: All 10 women who conceived showed 2 or within 2 days in-phase endometrial biopsies on days 7 to 11 after the LH surge. In 4 of 5 women biopsied on day 12, an unequivocally delay in the stroma was found, i.e., a persistence of edema and poor development of predecidual reaction. Since serum P levels in conception cycles were significantly higher than in nonconception cycles on days 10, 11, and 12, we interpreted this delay in the stroma as a consequence of conception.
Conclusion: Endometrial specimens during the last half of the luteal phase of conception cycles are in-phase until day 12. On day 12, gestational hyperplasia causes apparent out-of-phase.