Base Infertile Pattern (BIP)

The Base Infertile Pattern (BIP) is a woman's own baseline of dryness or unchanging discharge before Peak, when pregnancy is unlikely.¹ The pattern stays the same, with no new features, for consecutive days.

The concept began in the Billings Ovulation Method, under the name Basic Infertile Pattern. NaProTechnology and the Creighton Model, developed by Dr. Thomas W. Hilgers, use the same concept under the name base infertile pattern. Many women cannot apply a simple dry-day rule. For this reason, Billings teaches each woman to identify her own baseline over several consecutive cycles.

The pattern must repeat for several consecutive cycles. Only then can the woman and her practitioner confirm it as her BIP. Once the BIP is confirmed, any day that matches it counts as infertile.

Any change from the BIP marks the Point of Change. That change signals the opening of the fertile window.

The BIP matters most for women whose mucus stays the same across much of their mucus cycle. This group includes women who are postpartum, breastfeeding, coming off suppressive medications, or in perimenopause. For these women, the standard method of identifying the fertile window fails.

The BIP restores a clear reading of the chart. It ties the fertile window to a change from the woman's own baseline, rather than to a rigid rule.

The Creighton Model uses the same term. It adds the Essential Sameness Pattern and Yellow Stamps as its charting tool for unchanging discharge. In both systems, identifying the BIP requires several cycles of charting and instruction from a trained practitioner. The BIP is a tool for reading the body's own signal accurately, not for overriding it.