1. The normal cervical dilatation pattern in late pregnancy and labor;Hendricks;Am J Obstet Gynecol,1970
2. Williams' Obstetrics,1980
3. Labor: Clinical Evaluation and Management;Friedman,1978
4. Primigravid labor: A graphicostatistical analysis;Friedman;Obstet Gynecol,1955
5. Characteristics of normal labor;Kilpatrick;Obstet Gynecol,1989