1. Campbell H. Natural family planning in the;Ryder;Lancet,1990
2. It makes sense and empowers couples;Jarvis;BMJ,1993
3. Breastfeeding and the symptothermal method;Stud Farn Plann,1995
4. Symptoms and hormonal changes accompanying ovulation;Billings;Lancet,1972
5. The effectiveness phase;Fertil Steril,1981