Objective: To describe endometrial wavelike: activity. endometrial thickness and texture in IVF cycles, and to relate them to IVF outcome. To evaluate wave patterns on the day of hCG administration as a predictor of IVF outcome. Design: Ultrasound study. Setting: University hospital-based infertility clinic. Patient(s): Twenty-eight women undergoing IVF. Intervention(s): Ultrasound examinations were performed at live fixed moments (start ovarian stimulation, hCG administration, ovum pickup (OPU), ET, and 7 days after hCG administration) and at three variable moments in the stimulation period in the cycle. The OPU was performed 2 days after hCG administration; FT was performed 2 or 3 days after that. Main Outcome Measure(s): Endometrial wave pattern, thickness, texture, IVF outcome. Result(s): Embryo transfer was performed in 22 cycles. In 73% of the cycles a wave direction switch (WDS) from fundus to cervix (FC) to cervix to fundus (CF) occurred before OPU. Eleven (50%) patients became pregnant. Significantly more FC waves persisted until hCG administration in the cycles in which the patients conceived. Endometrial thickness and texture were unrelated to IVF outcome. Conclusion(s): Endometrial wave pattern is associated with pregnancy in IVF. The persisting presence of FC waves until hCG administration (a late WDS) predicts a favorable IVF outcome. (Fertil Steril(R) 1999;71:476-81. (C)1999 by American Society for Reproductive Medicine.).