During the 1950's, there was a priest (named Fr. Maurice Catarinich) in Melbourne, Australia, who was working with a group of women who had been using Calendar Rhythm. They said, “We want to be good Catholics, but a baby every 9 to 12 months is a little often. We would like to space our children a little more if you don’t mind.” Well, the priest, not having a background in reproductive biology did not know what to do, so he asked a parishioner, Dr. John Billings, if he would help him find something that these women could use to space their children.
In his research of medical journals, Dr. Billings found references to a mucus discharge, which originates from the cervix, in studies dating as far back as 1855. He asked these women if they ever saw this and they said, yes, but what is it? He began to have the women observe and record this mucus sign and found that there was a very distinctive pattern. It would start out as white and pasty and progress to become clearer and more like egg whites, and then it would disappear. Every woman had it and it was cyclic, but he did not know why it was there.
After 3 to 5 years of exhaustive research with Dr. James Brown, an endocrinologist, it was discovered that the pattern could be correlated with the estrogen and progesterone hormones of the woman’s cycle. They found that this discharge is only present during the time of fertility and that it is essential to a woman's fertility. Without it, a woman can not achieve a pregnancy.
Natural Family Planning simply teaches the couple how to recognize and record this sign of fertility and teaches the couple how to interpret and apply the specific guidelines for avoiding or achieving pregnancy.