As you approach your due date, you'll likely experience increased vaginal secretions and possibly even urine leakage from time to time. Unlike the usual increase in vaginal secretions, you may notice a thick, mucus-like discharge -- perhaps with a bit of blood. This type of discharge usually means that your mucus plug has started to come out of your cervix. This is a normal sign that you are nearing the end of pregnancy.
The Mucus Plug
To keep bacteria from entering the uterus and possibly infecting your baby or the uterus itself during pregnancy, nature has provided the perfect barrier between the vagina and uterus: a honeycomb-like web of thick mucus that fills the cervix. The cervix is the cylinder-like tissue between the lower end of your uterus and vagina. It opens, or dilates, during labor to allow your baby to pass into the world. The mucus plug fills the inside of the cervix. The mucus itself appears to have antibacterial properties that also reduce the risk of bacteria passing into the uterus, note the authors of an article in the April 2013 issue of "Acta Obstetricia et Gynecologica Scandinavica."
Mucus Plug Loss
During pregnancy, your cervix is approximately 1 to 2 cm long. As the end of pregnancy approaches, it begins to soften, thin and dilate. At the time of delivery, the cervix has thinned to about the thickness of a piece of paper and dilated to 10 cm. Thinning of the cervix, called effacement, generally occurs before dilation. Your cervix might also dilate as much as 3 cm before the start of labor, especially if you've had other children.
As the cervix thins, the mucus plug is squeezed out. It passes through the vagina and appears as a slimy discharge. Because the cervix often begins to dilate slightly before labor starts, microscopic blood vessels in the cervix can bleed. This can give the mucus plug a blood-tinged look.
What It Means
The appearance of the mucus plug doesn't necessarily mean that labor is on the verge of starting. Changes in the cervix can begin up to a month before delivery. You could lose part of your mucus plug several days before your labor starts. However, in many cases, labor begins within 24 to 48 hours of losing your mucus plug, according to the textbook "Maternity Nursing Care." In some cases, having sex or a vaginal exam could cause you to lose part of the mucus plug.
If you start to lose your mucus plug before the last month of pregnancy, your cervix might be dilating early. This puts you at risk for preterm delivery. Let your doctor know, even if there is no blood mixed in with the mucus. Passing rubbery blood clots could mean you are bleeding inside the uterus or vagina. Call your doctor right away if this occurs.