1. Department of Obstetrics and Gynecology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700‑8558, Japan
2. Department of Obstetrics and Gynecology, Kurashiki Medical Center, Kurashiki, Okayama 710‑8522, Japan
3. Department of Human Morphology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700‑8558, Japan