Thinking that NFP cannot work due to irregular menses is predicated on the old "Rhythm Method." Unfortunately, the pharmaceutical companies perpetuate this with their products designed to replicate the "normal cycle." Ovulatory cycles range from 26 to 35 days and do not obey calendars.
The great news is that the same researchers who brought the birth control pill to the market in 1960 have spent their careers researching natural fertility regulation. Please recommend the WOOMB website to your daughter (www.woomb.org ) and click on the OMRRC (Ovulation Method Reference and Research Center) for the history and research behind the simplest and most scientifically pure NFP method. All women, despite their reproductive history or stage in life can easily identify the roughly 96 hours of fertility per month. The numerous studies cited will testify to the 99.5% effectiveness rate. Experts in my field quote a pregnancy rate of 10% with typical use of the pill (Trussell, Pearl Index).
More importantly, if cycles are irregular, there is usually an underlying metabolic disorder which lies undiagnosed with typical gynecologic treatment. The Billings Ovulation Method chart is a bioassay of the ovarian hormones. This means that the charted changing or unchanging pattern of discharge is diagnostic and guides treatment. While there may be other NFP methods with varying detection methods, only the BOM chart reflects the actual production of estrogen and progesterone. One million hormonal assays and 55 years of research confirm this.
Mary W. Martin, M.D.,FACOG