Creighton Model FertilityCare System
The Creighton Model FertilityCare System (Creighton Model, FertilityCare, CrMS) is a form of natural family planning which involves identifying the fertile period during a woman's menstrual cycle. The Creighton Model was developed by Thomas Hilgers, the founder and director of the Pope Paul VI Institute.
Source: Wikipedia — Creighton Model FertilityCare System (CC BY-SA 4.0)