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Frank-Herrmann P, Heil J, Gnoth C, และคณะ (2007). "The effectiveness of a fertility awareness based method to avoid pregnancy in relation to a couple's sexual behaviour during the fertile time: a prospective longitudinal study". Hum. Reprod. 22 (5): 1310–9. doi:10.1093/humrep/dem003. PMID17314078.
Wade ME, McCarthy P, Braunstein GD, และคณะ (October 1981). "A randomized prospective study of the use-effectiveness of two methods of natural family planning". American Journal of Obstetrics and Gynecology. 141 (4): 368–376. doi:10.1016/0002-9378(81)90597-4. PMID7025639.
Medina JE, Cifuentes A, Abernathy JR, และคณะ (December 1980). "Comparative evaluation of two methods of natural family planning in Colombia". American Journal of Obstetrics and Gynecology. 138 (8): 1142–1147. doi:10.1016/S0002-9378(16)32781-8. PMID7446621.
Marshall J (August 1976). "Cervical-mucus and basal body-temperature method of regulating births: field trial". Lancet. 2 (7980): 282–283. doi:10.1016/S0140-6736(76)90732-7. PMID59854.
Frank-Herrmann P, Freundl G, Baur S, และคณะ (December 1991). "Effectiveness and acceptability of the sympto-thermal method of natural family planning in Germany". American Journal of Obstetrics and Gynecology. 165 (6 Pt 2): 2052–2054. doi:10.1016/s0002-9378(11)90580-8. PMID1755469.
Frank-Herrmann P, Freundl G, Gnoth C, และคณะ (June–September 1997). "Natural family planning with and without barrier method use in the fertile phase: efficacy in relation to sexual behavior: a German prospective long-term study". Advances in Contraception. 13 (2–3): 179–189. doi:10.1023/A:1006551921219. PMID9288336.
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Howard, M.P.; Stanford, J.B. (1999). "Pregnancy probabilities during use of the Creighton Model Fertility Care System". Archives of Family Medicine. 8 (5): 391–402. doi:10.1001/archfami.8.5.391. PMID10500511.
James B. Brown (2005). "Physiology of Ovulation". Ovarian Activity and Fertility and the Billings Ovulation Method. Ovulation Method Research and Reference Centre of Australia. คลังข้อมูลเก่าเก็บจากแหล่งเดิมเมื่อ 2005-12-24.
James B. Brown (2005). "Physiology of Ovulation". Ovarian Activity and Fertility and the Billings Ovulation Method. Ovulation Method Research and Reference Centre of Australia. คลังข้อมูลเก่าเก็บจากแหล่งเดิมเมื่อ 2005-12-24.
Dunson, D.B.; Baird, D.D.; Wilcox, A.J.; Weinberg, C.R. (1999). "Day-specific probabilities of clinical pregnancy based on two studies with imperfect measures of ovulation". Human Reproduction. 14 (7): 1835–1839. doi:10.1093/humrep/14.7.1835. ISSN1460-2350.