The mucus symptom is recorded under the following three parameters:

  • Sensation
  • Appearance
  • Quantity

Where is mucus produced?

Oestrogenic mucus is secreted in cells in the cervical crypts under the stimulation of oestrogen on the six days leading up to ovulation, i.e. in the fertile phase of the cycle.

Where is mucus perceived?

As the woman goes about her daily activities she perceives the sensation of the presence of mucus at the opening of the vagina, (called the vulva).3  The vulva can sense the presence of as little as 5mg of mucus, while 40mg of mucus are needed to obtain enough mucus for visual inspection.3

NOTE: The ‘sensation’ parameter is very useful for those women who are blind, as they can readily perceive the changes in sensation at the vulva during the cycle.

What sensation is perceived at the vulva in the infertile phase of the cycle?

When ovarian activity is absent and no oestrogen is being produced there is usually no mucus discharge and the sensation is one of dryness at the vulva which persists throughout the period of ovarian inactivity, i.e. during the infertile phases of the cycle.1

How is the change to a mucus discharge perceived?

The beginning of the mucus discharge signals the beginning of the fertile phase of the cycle and is perceived by the woman as a sensation of stickiness, moistness or dampness at the vulva. Over the six days of the mucus discharge the sensation changes to one of wetness and slipperiness at the time of maximum fertility just before ovulation.3
During these six days the appearance of the mucus also changes from a thick, opaque appearance at first to become clear and stretchy like raw-egg-white at maximum fertility just before ovulation.
While the woman is recumbent as when in bed sleeping, the discharges do not drain away so that the woman has to be some time in the upright position for the sensation to be appreciated, and the mucus discharge to be seen, and its appearance and quantity noted.

  • The perception of mucus occurs at the surface of the labia minora of the vulva. (see Fig 8A, page 2 of Pictures & Diagrams ). The total area of the labia minora sensitive to the presence of mucus, changes with age and parity. It increases slowly from early adolescence to the fourth decade and also during pregnancy, and it is decreased in women on hormonal contraception, and this may cause difficulty in identifying the mucus symptom after stopping the ‘Pill’.2 Marked atrophy of this area can occur in the menopause.2  

When should the woman look for mucus?

The woman should look for mucus at the vulva at each visit to the toilet. She observes before and after passing urine by wiping from front to back over the vulva, (i.e. the opening of the vagina) with soft white toilet tissue. A finger- tip can be applied to the mucus on the tissue and then pulled gradually away to test its capacity to stretch. She observes:

  • The Sensation – What does she feel, is the tissue pulling over the perineum? Is it slipping over the perineum?

(NOTE: the sensation of mucus is perceived at the vulva by the woman as she goes about her normal daily activities over the whole day).

  • The Appearance – What does she see on the tissue? The colour and texture of mucus? Is it thick and opaque, or clear and stretchy ?

Should various types of mucus be observed, the most fertile type of mucus observed over the whole day should be recorded on the chart each evening. The study by the World Health Organization (W.H.O.) found that more than 90% of women could identify the mucus symptom correctly in the first month of learning.3,4


  • The mucus symptom is observed at the vulva.
  • Look for mucus before and after passing urine.
  • Observe mucus by its sensation and appearance.
  • Observe mucus through the day and record each night the most fertile type observed during the day.


  1. Brown, JB; ‘Ovarian activity and fertility and the Billings Method’ (interenet; Billings Life; 2005)
  2. Odeblad E, ‘Investigations on the physiological basis for fertility awareness’ page 7; Bulletin for the Ovulation Method Research and Reference Centre of Australia, vol 29, no 1, p2-11, march 2002, (internet, Billings Ovulation Method,
  3. Klaus, Hanna; ‘Natural family planning – Is it scientific? Is it effective?’ see page 9,8,12; Newman Lecture Series 1-May 21, 2000. (online).
  4. World Health Organization; ‘A prospective multi-centre trial of the Ovulation Method of Natural Family Planning 1; The Teaching Phase’; Fertility & Sterility; Vol. 36, no 2, Aug 1981; pages 152-158.