The Role of the Mucus Plug in Pregnancy and Labor

If the word "mucus" makes you squeamish, you're not alone. But believe it or not, mucus and the mucus plug are important in conception and pregnancy.

Mucus is produced during ovulation to help sperm pass through the cervix and provide them with an ideal environment before fertilizing an egg. Once fertilization occurs, the mucus changes to seal the cervix—with what we call the mucus plug—and protect the fetus from infection.

Without the mucus plug, maintaining a pregnancy to term would be unlikely and, in some cases, impossible.

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.

The mucus plug is roughly the size of a quarter and made up of around two tablespoons of mucus. It is generally a creamy to yellowish-white color and may sometimes be streaked with pink. It can also sometimes be more beige, or even brown, in color. This is not unusual and shouldn’t cause concern.

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.

It is impossible to predict when the mucus plug will be passed as it varies from woman to woman and pregnancy to pregnancy. In many cases, the passing will be evidenced by pieces of mucus found in the woman’s panties or bedsheets. Some women may not even notice it at all, because it was passed during urination or while showering.

There is typically little, if any, pain when the mucus plug is passed. Some women will complain of nagging pain in the lower abdomen similar to menstrual cramping, though this is less common.

When the plug is passed, it doesn’t necessarily mean that labor is imminent. At times, labor may begin in a few hours; at others, it may take several weeks.

You'll also want to watch for known symptoms of imminent labor, such as lightening (when the baby drops lower into the pelvis), the beginning of regular contractions, and when your water breaks.

Losing your mucus plug also doesn’t mean that your baby is suddenly at increased risk of infection. By this stage in the pregnancy, the amniotic fluids in the gestational sac offer 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.

However, 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.