What Is the Mucus Plug?

Illustration of mucus plug

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What Is the Mucus Plug?

The mucus plug is created once fertilization of an egg occurs. The mucus seals the cervix with what is called the mucus plug. This will protect the fetus from infection. Without the mucus plug, maintaining a pregnancy to term would be unlikely and, in some cases, impossible.

Why It's Important

The mucus plug is formed from secretions of cervical glands and has a thick, gelatinous consistency. The plug begins to form when the fertilized egg implants in the wall of the uterus. When this happens, the cervix softens and swells as mucosal cells start pumping mucus into the cavity until there are no gaps left.

Prompted by the hormone progesterone, the mucus thickens and continues to be secreted throughout pregnancy, so that the plug always remains fresh. Within this thick, sticky fluid are antibodies that can protect the growing fetus from many bacteria, viruses, and other disease-causing agents.

Before labor begins, the balance of a woman’s hormones starts to change. Estrogen levels rise as the process of fetal development nears completion. As a result, the plug starts to thin and the cervix gradually softens and dilates.

During this time, there may some discharge (which is typically odorless), or the plug may come out all at once. There may also be streaks of red or pink caused by the rupture of capillaries, which is why the loss of the mucus plug is sometimes referred to as the "bloody show."

The passing of the plug indicates that labor is nearing, regardless of the stage of pregnancy. Therefore, if the mucus plug is passed during early pregnancy, it may be the sign of impending preterm birth.

What to Look For

The mucus plug is roughly the size of a quarter and made up of around 2 tablespoons of mucus. Its appearance can vary somewhat:

  • It is generally a creamy to yellowish-white color and may sometimes be streaked with pink.
  • It may appear as bloody show—pink, brown, or red-tinged discharge that you notice on your underwear or toilet paper after you urinate.
  • It can also sometimes be more beige, or even brown, in color. This is not unusual and shouldn’t cause concern.

It is impossible to predict exactly when the mucus plug will be passed, as it varies from woman to woman and pregnancy to pregnancy.

A few different things may happen when you lose your mucus plug:

  • You may notice it. In many cases, the passing will be evidenced by pieces of mucus found in your undergarments or bedsheets. It can be released over a few days.
  • You may not notice it. For some women, the mucus plug is passed during urination or while showering.
  • You may feel mild cramping. Some women will complain of nagging pain in the lower abdomen similar to menstrual cramping, though this is less common.

If you happen to be aware of when your mucus plug comes out or you notice bloody show, it could mean that labor is just a few hours away—or it could mean you still have weeks to go. 

Losing Your Mucus Plug Early

Losing your mucus plug prior to week 37 of pregnancy is not necessarily a sign of miscarriage. In fact, many women experience vaginal discharge and even light spotting and go onto have a healthy pregnancy.

It also doesn’t mean that your baby is suddenly at increased risk of infection. By late pregnancy, the amniotic fluid in the gestational sac offers ample protection right up until the time your water breaks.

Once you have lost your mucus plug, you do not need to make any special accommodations, such as avoiding sex or baths. It is only when your water breaks that your baby starts becoming at risk of infection.

Losing your mucus plug early, however, may mean you're going into labor early. Knowing the signs of preterm labor as well as miscarriage can help you determine when to contact your doctor:

Symptoms of preterm labor include:

  • Bright red blood from your vagina
  • Contractions or cramps, more than five in one hour
  • Intense pelvic pressure
  • Low, dull backache
  • Sudden gush of clear, watery fluid from your vagina

Signs of miscarriage (pregnancy loss before the 20th week) include:

In addition, warning signs of stillbirth (pregnancy loss after the 20th week) include:

  • Not feeling the baby kicking
  • Persistently low number of kicks, or a dramatic increase
  • Severe abdominal or back pain
  • Vaginal bleeding

If you experience any of these symptoms, call your practitioner right away. You should have an emergency number but, if not, go to the nearest emergency room for care.

A Word From Verywell

When the mucus plug is passed, it is usually a good idea to call your doctor or midwife to ensure that everything is OK and to get a better idea of when you can expect to deliver. This is especially important if you lose the plug prior to 37 weeks of pregnancy.

If the passing of the plug is accompanied by heavy bleeding or a deep red discharge, call your doctor immediately, as these can be a sign of potential complications.

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Article Sources
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  1. Becher N, Adams-Waldorf K, Hein M, Uldbjerg N. The cervical mucus plug: Structured review of the literature. Acta Obstet Gynecol Scand. 2009;88(5):502-13. doi:10.1080/00016340902852898

  2. Critchfield AS, Yao G, Jaishankar A, et al. Cervical mucus properties stratify risk for preterm birth. PLoS ONE. 2013;8(8):e69528. doi:10.1371/journal.pone.0069528

  3. American College of Obstetricians and Gynecologists. Preterm labor and birth. Updated June 2007.

  4. American College of Obstetricians and Gynecologists. Early pregnancy loss. Updated August 2015.