Luteal phase abnormalities in early menstrual cycles after pregnancy have been shown to cause confusion in the practice of natural family planning (NFP) for some patients and to restrict severely the number of late infertile days available to others. The cause of the abnormalities is uncertain but appears to be related to the nursing status of the patient.
Hatherley LI, 1985Clinical Reproduction and Fertility
A prospective six-year study (1975-1980) of 273 patients, monitored in the use of natural family planning (NFP), has shown that those with previously irregular menstrual cycles are disadvantaged in th...