Key references: Symptom-based methods of contraception
- American College of Obstetricians and Gynecologists (ACOG). Fertility awareness-based methods of family planning. Frequently asked questions: contraception. Washington DC: ACOG; 2019. https://www.acog.org/patient-resources/faqs/contraception/fertility-awareness-based-methods-of-family-planning
- Arevalo M, Jennings V, Nikula M, Sinai I. Efficacy of the new TwoDay method of family planning. Fertil Steril 2004;82(4):885–92. https://www.ncbi.nlm.nih.gov/pubmed/15482764
- Bhargava H, Bhatia JC, Ramachandran L, Rohatgi P, Sinha A. Field trial of billings ovulation method of natural family planning. Contraception 1996;53(2):69–74. https://www.ncbi.nlm.nih.gov/pubmed/8838482
- Fehring RJ, Lawrence D, Philpot C. Use effectiveness of the Creighton model ovulation method of natural family planning. J Obstet Gynecol Neonatal Nurs 1994;23(4):303–9. https://www.ncbi.nlm.nih.gov/pubmed/8057183
- The Faculty of Sexual & Reproductive Healthcare (FSRH) Clinical Effectiveness Unit. FSRH Clinical guidance: Fertility awareness methods. London: FSRH; 2015. https://www.fsrh.org/standards-and-guidance/documents/ceuguidancefertilityawarenessmethods/