Vollmar, A. K. R., Mahalingaiah, S., & Jukic, A. M. (2025). The menstrual cycle as a vital sign: A comprehensive review. F&S Reviews, 6(1), 100081. https://doi.org/10.1016/j.xfnr.2024.100081
Padilha, T., & Deretti, E. A. (2021). Billings Ovulation Method: Between efficacy and lack of knowledge. Revista Bioética, 29(1), 208–219. https://doi.org/10.1590/1983-80422021291460
Vigil, P., Blackwell, L. F., & Cortés, M. E. (2012). The importance of fertility awareness in the assessment of a woman’s health: A review. The Linacre Quarterly, 79(4), 426–450. https://doi.org/10.1179/002436312804827109
McSweeney, L. (2011). Successful sex pre-selection using natural family planning. African Journal of Reproductive Health, 15(1), 79–84.
Attar, E., Gokdemirel, S., Serdaroglu, H., & Coskun, A. (2002). Natural contraception using the Billings ovulation method. The European Journal of Contraception & Reproductive Health Care, 7(2), 96–99. https://doi.org/10.1080/ejc.7.2.96.99
Xu, J. X., Yan, J. H., Fan, D. Z., et al. (1994). Billings natural family planning in Shanghai, China. Advances in Contraception, 10, 195–204. https://doi.org/10.1007/BF01983351
Perez, A., Labbok, M., Barker, D., & Gray, R. (1988). Use-effectiveness of the ovulation method initiated during postpartum breastfeeding. Contraception, 38(5), 499–508. https://doi.org/10.1016/0010-7824(88)90154-0
World Health Organization. (1983). A prospective multicentre trial of the ovulation method of natural family planning. III. Characteristics of the menstrual cycle and of the fertile phase. Fertility and Sterility, 40(6), 773–778. https://doi.org/10.1016/S0015-0282(16)47478-9
Pérez, A., Zabala, A., Larraín, A., Widmer, S., Núñez, M., Baranda, B., Barros, G., Carrasco, M., & Cabezón, C. (1983). Eficacia clínica del método de la ovulación (Billings). Revista Chilena de Obstetricia y Ginecología, 48(2), 97–107.
World Health Organization. (1981). A prospective multicentre trial of the ovulation method of natural family planning. II. The effectiveness phase. Fertility and Sterility, 36(5), 591–598. https://doi.org/10.1016/S0015-0282(16)45856-5
World Health Organization. (1981). A prospective multicentre trial of the ovulation method of natural family planning. I. The teaching phase. Fertility and Sterility, 36(2), 152–158. https://doi.org/10.1016/S0015-0282(16)45671-2
Klaus, H., Goebel, J., Woods, R. E., Castles, M., & Zimny, G. (1977). Use-effectiveness and analysis of satisfaction levels with the Billings ovulation method: Two-year pilot study. Fertility and Sterility, 28(10), 1038–1043. https://doi.org/10.1016/S0015-0282(16)42851-7
Ball, M. (1976). A prospective field trial of the ‘ovulation method’ of avoiding conception. European Journal of Obstetrics & Gynecology and Reproductive Biology, 6(2), 63–66. https://doi.org/10.1016/0028-2243(76)90004-6
Flynn, A. M., & Lynch, S. S. (1976). Cervical mucus and identification of the fertile phase of the menstrual cycle. British Journal of Obstetrics and Gynaecology, 83, 656. https://doi.org/10.1111/j.1471-0528.1976.tb00906.x
Weissmann, M. C., Foliaki, L., Billings, E. L., & Billings, J. J. (1974). A trial of the ovulation method of family planning in Tonga. The Lancet, 1, 813. https://doi.org/10.1016/S0140-6736(72)92164-2
Billings, E. L., Brown, J. B., Billings, J. J., & Burger, H. G. (1972). Symptoms and hormonal changes accompanying ovulation. The Lancet, 299(7745), 282–284. https://doi.org/10.1016/S0140-6736(72)90291-7
