Important natural signs of fertility that are used in many different methods of NFP are the changes in the characteristics of cervical mucus and the resulting vulvar sensations. Cervical mucus changes its characteristics during the menstrual cycle and can provide the woman observer information about the beginning, peak, and end of the fertile phase.
Cervical mucus changes are a result of the developing egg and follicle in the ovary. When a follicle (with the egg inside) starts to grow early in the menstrual cycle, it begins to produce estrogen. Estrogen stimulates the cervix to produce mucus. Beginning cervical mucus is thick, sticky, and holds its shape. The opening of the cervix at this time also begins to soften and widen. As the follicle grows and ripens more estrogen is produced, and the cervical mucus changes to a cloudy, thinner, and a slightly stretchy type mucus. Fertility is high at this time. Right before ovulation, the follicle is at its largest and produces the most estrogen, cervical mucus at this time is very clear, stretchy, watery, and slippery (like egg white). The cervix is also very soft, and the opening widens. Cervical mucus pours out from the cervical opening. The woman is at the peak of her fertility at this time.
After ovulation, when the egg is released from the follicle, the follicle changes into a structure called the corpus luteum. The corpus luteum produces the female hormone progesterone. Progesterone heats up the woman’s body about 0.4 to 0.8 degrees, causes the cervical mucus to dry up and the cervix to close and tighten. The cervical mucus again becomes very thick, cloudy, and forms a plug at the opening of the cervix. When this happens fertility is again at a low level.
A woman who observes her mucus on a daily basis will be able to observe these changes and know that the beginning of her fertility occurs when mucus is first felt or seen. Her fertility is high when the mucus becomes slightly stretchy and thinner. The peak of her fertility occurs when the mucus is very clear, stretchy, and slippery. The end of her fertility begins three full days after the last day she observes peak type mucus. She will only know the Peak day of cervical mucus retrospectively.
The figure ABOVE shows a typical mucus cycle going from minimal, progressing to stretchy cloudy, then to peak and back again to tacky cloudy type mucus.
Mucus cycles will vary from woman to woman and from cycle to cycle.
Fig. 7: Beginning fertile mucus = Low Fertility
Figure 7 shows how cervical mucus might look at the beginning of the mucus cycle (the beginning of the fertile phase). When a woman observes mucus she can feel for the sensation and observe its characteristics. Many women observe cervical mucus by finger testing, lifting mucus off of a tissue and observing it at eye level between the finger and thumb. Early cervical mucus usually feels moist or sticky, and appears scant, thick, minimal, white, and holds its shape. When a woman observes this type of mucus or has no mucus and a dry sensation, she is at LOW fertility.
Fig. 8: Transitional cervical mucus = High Fertility
As the cycle progresses and more estrogen is secreted by the growing follicle, the mucus increases in amount, becomes thinner, cloudy, slightly stretchy. The texture of the mucus might also change from moist and sticky to wet. When mucus is observed with these characteristics it is considered a sign of HIGH fertility.
Fig. 9: Peak fertile mucus = Peak Fertility
The peak of fertility during the menstrual cycle occurs when peak type mucus is present. Mucus at this time has a very slippery (lubricative) sensation. It appears transparent, clear, is very stretchy and looks similar to raw egg white. At the peak of fertility, cervical mucus is very profuse and literally pours out of the cervix over a 24-hour period. Sometimes the mucus is so watery that there is no mucus to pick up, and the women will only notice a very wet, slippery sensation.
The PEAK DAY of cervical mucus: The last day of any mucus that is clear (transparent), stretchy, and/or has the sensation of slippery is considered the peak of cervical mucus and the Peak day. After the Peak day there is an obvious change to sticky, tacky, cloudy type mucus or to dry (i.e., no mucus appears at the vulva, and there is a dry sensation). Therefore, the Peak day will only be known retrospectively! Fertility is High for 3 full days after the Peak day of cervical mucus.