Creighton Model FertilityCare System of NFP is sometimes called a "single index" method because it solely relies on the woman's observations of mucus to determine her fertility.This model uses a standardized observation and charting of biological markers (cervical mucus) that are essential to a woman’s health and fertility. These “biomarkers” tell the couple when they are naturally fertile and infertile, allowing the couple to use the system either to achieve or to avoid pregnancy. This system also works closely with NaPro technology to be able to identify and treat women’s health issues such as infertility, PCOS, irregular bleeding, repeated miscarriage, and postpartum depression.
In it's effectiveness study (Hilgers & Stanford, 1998), Creighton Model System of NFP was found to be between 94.6(typical use) up to 99..8 % (perfect use) effective. This means that out of a group os 100 women, somewhere between 1-6 of them may become pregnant while using the method to avoid a pregnancy. Each method will have their own effectiveness rates and you can find many of them in this study.