Kaminski P F, Meilstrup J W, Ekbladh L E, Shackelford D P, Thieme G A
Department of Obstetrics and Gynecology, Pennsylvania State University, Milton S. Hershey Medical Center, Hershey 17033.
J Ultrasound Med. 1994 Nov;13(11):911-5. doi: 10.7863/jum.1994.13.11.911.