Can NFP be used only by women with regular cycles?

NFP can be used by any woman regardless of the length or variations in her cycle. NFP is effective with menstrual cycles of any length and any degree of irregularity such as during breastfeeding, pre-menopause, and other special circumstances. Modern NFP methods monitor the current, day-to-day signs of fertility and/or infertility. These body signs are specific and observable.

NFP allows a woman to understand her body's physical signals telling her when she is most likely to become pregnant. Knowing this, she and her spouse can effectively avoid or achieve a pregnancy.