A Key Fertility Sign: Cervical Mucus

What is cervical mucus?

Cervical mucus is a whitish or clear vaginal discharge which, in the average 28 day menstrual cycle, is first noticed by the woman about 4 days after menstruation has stopped. This vaginal discharge comes from glands in the cervix, (i.e. the lower end of the uterus), it persists for about six days and then dries up abruptly after ovulation.

Why is cervical mucus important? 

Cervical mucus is important for two reasons,

  • because of its function in relation to sperm
  • because it is the most important indicator of impending ovulation

What is the function of cervical mucus in relation to sperm?

Fertile-type cervical mucus is required:

  • to nourish sperm, (sperm can survive for up to five days in fertile-type mucus)
  • to transport sperm to the uterus
  • to attract sperm
  • to filter sperm.

Why is cervical mucus an important indicator of impending ovulation?

When the woman perceives the beginning of the mucus symptom she knows that the fertile phase of the cycle has begun. The mucus symptom is the most important fertility indicator used in natural family planning, its presence is a sign of potential fertility as it indicates that the ovum (egg) is developing in the ovary and it is therefore an indicator of impending ovulation.

Is cervical mucus essential to achieving pregnancy?

The presence of cervical mucus is essential to achieve pregnancy, indeed pregnancy cannot occur without the presence of mucus. This is because fertile-type mucus nourishes sperm and transports sperm to the uterus. Sperm can survive for up to five days in fertile-type mucus. Cervical Mucus also attracts and filters sperm. This function of attracting and transporting sperm is why those couples who wish to avoid pregnancy and who use natural family planning are advised to avoid all genital contact during the fertile phase of the cycle as pregnancies have been known to occur even without penetration due to the presence of fertile-type mucus at the opening of the vagina. (see WHO Definition)

Does the mucus symptom always start about four days after menstruation?

The mucus symptom does not always start 3 or 4 days after menstruation has ended; it depends on the length of the cycle. For example if the cycle is very short the mucus symptom may start before menstruation has finished, and if the cycle is long the mucus symptom may start perhaps 10 or more days after menstruation has stopped This is because the mucus symptom is present on the six days leading up to ovulation and ovulation does not always occur on the same day in every cycle.

When does ovulation occur?

Ovulation, (release of an egg), usually occurs about 14 days before the next menstruation. The part of the cycle after ovulation has a constant length of 14 days on average; therefore if the woman has a menstrual cycle that is longer or shorter than usual it is the part of the cycle before ovulation that is longer or shorter. In long cycles the beginning of the mucus symptom occurs later, and in short cycles the mucus symptom may start immediately after menstruation has ended, or indeed may overlap menstruation.


Acknowledgement: Articles on cervical mucus and natural family planning by Professor Erik Odeblad, Dr Hanna Klaus, Dr Kevin Hume, and Professor JB Brown are quoted extensively in these pages on Cervical Mucus. These articles are available free on the internet and the authors are due much thanks for sharing their knowledge and expertise so generously.

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