1. Natural Family Planning -- www.everettclinic.com
They wish to use a "natural" method of birth control that does not involve medications, surgery, or devices. Their religious beliefs prohibit the use of other methods of birth control. A couple may use fertility awareness for birth control if:.
http://www.everettclinic.com/kbase/topic/medtest/hw214032/whydone.htm

2. Abstinence, periodic -- Information from MedicineNet
Abstinence, periodic definition - Medical Dictionary definitions of popular medical terms. medical dictionary A-Z List > Abstinence, periodic. Online Medical Dictionary and glossary with medical definitions.
http://www.medterms.com/script/main/art.asp?articlekey=9772

3. Natural Family Planning -- Health Information for the Whole Family
Natural Family Planning -- familydoctor.org. Information about natural family planning from the American Academy of Family Physicians. familydoctor.org Home Women Natural Family Planning. Two methods of natural family planning are currently taught.
http://familydoctor.org/126.xml