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Diakses pada 14 September 2020Planned Parenthood. https://www.plannedparenthood.org/learn/birth-control/fertility-awareness/whats-calendar-method-fams
Diakses pada 14 September 2020Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/womens-health/in-depth/menstrual-cycle/art-20047186
Diakses pada 14 September 2020Healthline. https://www.healthline.com/health/how-to-regulate-periods
Diakses pada 14 September 2020Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/womens-health/in-depth/menstrual-cycle/art-20047186
Diakses pada 14 September 2020