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Reviewed by the Faculty of Harvard Medical School

Cervical-Mucus Monitoring

Clues about ovulation can be gathered from the appearance and quality of the cervical mucus. As ovulation approaches, the cervical mucus thins and becomes increasingly elastic and transparent. By monitoring cervical-mucus changes you can predict when ovulation is likely to happen so you know when to avoid intercourse. Sometimes this form of birth control is referred to as the Billings method.

You should observe your cervical mucus every day, beginning the first day after your last period. Cervical mucus may be found by wiping your vagina before urinating, inserting your clean finger into your vagina, or simply noting its presence on underwear. Regardless of which technique you choose, there is almost no mucus found immediately after your period stops.

It's OK to have intercourse in these early days after your period, but sometimes the semen from intercourse can be confused with mucus because seminal fluid can have a whitish, thick appearance. When you see the cervical mucus first appear, you should avoid sexual intercourse especially when the mucus becomes more abundant, thin, transparent and slippery, like egg whites, as ovulation approaches.

You shouldn't resume sex for at least three days after the disappearance of the slippery mucus, when it becomes more opaque and sticky.

With this method, the fertile time is between the first day of a period until three days after the disappearance of the slippery, more transparent cervical mucus. Note, sexual intercourse is best avoided during menstruation, yet it is permitted days just before ovulation until the cervical mucus is present.


  • Perfect practice of this method results in an approximately 3 percent rrate of pregnancy in the first year of use.
  • This method does not cost anything, and there is no need for medications or surgery.
  • This method does not interrupt or alter fertility. Pregnancy is possible as soon as this method is abandoned.


  • When used imperfectly, this method has a pregnancy rate as high as 84 percent.
  • Because of normal variations in the menstrual cycle and in the lifespan of eggs (one to three days) and sperm (two to seven days), you will need to abstain from intercourse for a number of days, including those immediately around ovulation, to be safe.
  • This method is less reliable when cervical mucus is abnormal or unusual, as in the following situations:
    • Women who are breast-feeding
    • Women who have cervical or vaginal infections
    • Women who have had recent surgery of the cervix
    • Women who recently took birth-control pills
    • Women who use contraceptive foams, jellies or feminine-hygiene products
    • Women nearing menopause

Last updated October 1, 2010