The mucus plug consists of mucins, which are glycoproteins that form at the cervix to protect the fetus from infections and preterm labor.

The mucus plug, which weighs approximately 10 grams, is formed during pregnancy and is shed when labor is near. Without the formation of the mucus plug, pregnancy likely will not continue. The shedding of the mucus plug is often a sign that labor and delivery could occur soon.

Purpose

Once fertilization occurs, a thick gelatinous mass forms at the opening of the cervix from excretions from the mucosal cells in the cervix. This mass, known as the mucus plug, contains properties that prevent viruses from replicating and stop bacteria from spreading.

The mucus plug can also initiate an immune response that helps the body fight off any impending bacterial infection, which is a primary cause of preterm labor.

These properties set it apart from the cervical secretions of people who are not pregnant.

Throughout pregnancy, the mucus plug is continuously refreshed with new secretions, in part due to the hormone progesterone.

Signs

Near the end of pregnancy, rising estrogen levels cause the cervix to open (dilate) and thin. This change can cause the mucus plug to dislodge and be excreted from the vagina. Since there is often an increase in discharge during pregnancy, it can be difficult to tell whether the mucus plug has been shed.

Signs that the mucus plug has been shed include:

• An increase in discharge that can be clear, creamy, yellow-white, pink-tinged, or streaked
• Red-tinged, pink, or brown discharge on your underwear or toilet paper, also known as bloody show
• Discharge appearing as beige or brown
• Stringy, or thick and gelatinous discharge, sometimes expelled all at once

Shedding of the mucus plug can occur after a cervical exam or after intercourse, but it should not be confused with seminal fluid.

The time between the shedding of the mucus plug and labor starting is different for each case. Sometimes the plug will be shed days or weeks ahead of labor beginning, and sometimes hours or during labor and delivery.

Other signs of labor are better indicators of whether delivery is near, including:

• Membrane rupture: Known as water breaking, the amniotic sac breaks, and a trickle or gush of fluid will leak from the vagina.
• Contractions: A regular pattern of often painful contractions in your pelvis and low back that gradually get closer together. 

As mentioned above, the mucus plug can be expelled over several days, and you may see evidence of it on your sheets, underwear, or in the toilet. However, it can be discharged without any noticeable signs.

If you have other symptoms of labor, you should contact your doctor, regardless of whether there’s evidence of the mucus plug or not.

Complications

The passing of the mucus plug occurs when labor and delivery are near, even if the pregnancy has not reached full term. Therefore, if the mucus plug is excreted before 37 weeks of gestation, preterm labor may occur and you should seek medical care.

The loss of the mucus plug before 37 weeks does not mean that miscarriage will occur or that you will get an infection, but your doctor will likely want to examine you to be sure. Try to keep a record of when you noticed signs of losing the mucus plug, what it looked like, and in what volume, along with any other signs or symptoms you might have.

When the mucus plug is expelled, it may mean that labor will occur. It is essential to know the signs of preterm labor and miscarriage.

Signs of preterm labor (between the 20th and 37th week of pregnancy) include:

• Mild to moderate cramping in your abdomen
• Dull low backache that is constant 
• Feeling pressure in your pelvis or lower abdomen
• Diarrhea 
• Contractions that are consistent and frequent, with or without pain
• Watery, bloody, or mucus discharge that is different than usual
• More discharge than usual
• Water breaking in a trickle or gush, signaling ruptured membranes

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

• Pain and cramping in your abdomen or low back
• Tissue passing from the vagina
• Bleeding from the vagina
• Sudden loss of other pregnancy symptoms

Later in pregnancy, the amniotic sac, filled with fluid, provides closure to the cervix until your water breaks. After 37 weeks gestation, if no other labor symptoms are present, then the loss of the mucus plug is not a concern.

A Word From Verywell

Although the mucus plug passing is not a sign that labor is starting right away, it is wise to let your doctor know so they can do a checkup, especially if you are less than 37 weeks pregnant. Once your mucus plug is expelled, it does mean that labor and delivery could be near. Watch for other signs like leaking fluid and regular contractions. 

Call your doctor or obstetric provider if you notice the mucus plug has been passed along with other symptoms like cramping, bleeding, or leaking fluid, as it could be a sign of complications.