Obstetrics and Gynecology, 53(1), 12-22
St. Louis University Natural Family Planning Center. St. Louis. Missouri and Creighton University Natural Family Planning Education and Research Center, Omaha. Nebraska
Hilgers, T. W., & Prebil, A. M. (1979). The ovulation method--vulvar observations as an index of fertility/infertility. *Obstetrics and gynecology*, *53*(1), 12-22.
Hilgers TW, Prebil AM. The ovulation method--vulvar observations as an index of fertility/infertility. Obstet Gynecol. 1979;53(1):12-22.
Hilgers, T. W., and A. M. Prebil. "The ovulation method--vulvar observations as an index of fertility/infertility." *Obstetrics and gynecology*, vol. 53, no. 1, 1979, pp. 12-22.
Cervix Mucus, Female, Fertility, Humans, Infertility, Female/diagnosis, Menstruation, Models, Biological, Natural Family Planning Methods, Ovulation, Vulva