This may be true of some methods, but Creighton can be relied on after one month of charting (regardless of regular or irregular cycles). It relies on cervical mucus which gives advance notice of ovulation instead of temperatures which only confirm things after the fact. The instructions of when to avoid evolve as the couple becomes more familiar with the method, but beginning instructions are provided after one month of charting.
Originally Posted by l_Kimmie_l
I was charting prior to AF comin back and got pregnant first PP 'o' due to it not being seen till after the temp rise and it is too late. I would not rely on this method alone till you are regular with AF/o again. You are supposed to use 3 months of charting with a regular cycle to determine when to avoid.
Creighton Model FertilityCare Teacher
Helping others to appreciate their fertility whether trying to avoid or conceive