Here is one I found on Wikipedia :
The Creighton Model teaches women to observe certain biological signs to monitor their own gynaecological health, and to identify times of fertility and infertility. These biological signs include cervical mucus and bleeding patterns, and can be observed and analysed in all types of menstrual cycles. These signs are charted daily to give a picture of the woman's individual cycle.

Doctors can use the fertility charts which couples are taught to keep as the basis for further investigations if needed.

Blood tests for Oestrogen levels prior to ovulation and for both Progesterone and Oestrogen levels after ovulation, ultrasound follicular tracking, and other diagnostic procedures, can be accurately timed according to the woman's cycle, using the data recorded on a couples' fertility chart. This allows doctors to make a more precise diagnosois of abnormalities, e.g. subtle hormonal deficiencies, various ovulation defects etc.

The Creighton Model was developed at the Pope Paul VI Institute which was itself set up to support medically the directives given by Pope Paul VI in his encyclical 'Humanae Vitae: On the Regulation of Birth'.
I really thought that part at the end was interesting to note....