In pregnancy, a woman's body develops protective systems to protect the baby in the womb. One of these is the mucous plug, which sits at the cervix -- the point where the uterus meets the vagina. It acts as a barrier to the entry of potentially dangerous microbes into the uterus while the baby is developing. Technically a mucous plug is called an "operculum," which means "little lid" in Latin. Most often, though, women either call it the mucous plug, or when it comes out, "the bloody show."
According to the NHS, the passing of a mucous plug is not necessarily a sign that a woman is going into labour. In fact, the plug can come away a few weeks before labour begins, just prior to the start of labour, or when the woman is in early labour. The East Sussex Healthcare NHS Trust states that women need not necessarily inform their midwife or doctor when the plug comes away, unless it appears abnormal.
The appearance of the mucous plug varies. For some pregnancies, it is clear. For others, it can contain new or old blood, so it can be pink, streaked with blood, or it can be red or brown. The blood is in the mucus only because as the cervix softens, some of the small blood vessels in it break open harmlessly as it becomes more stretchy. The plug can also be thick and sluglike, and can look like the thick discharge from the nose that can accompany a bad cold. Sometimes the plug comes out in one piece, sometimes it is stringy, and sometimes it comes away in little blobs over the course of several days. In addition, the mucus normally has no smell.
A normal mucous plug can contain a small amount of blood, and streaks of blood in the plug are also normal. If the mucus is very bloody, though, or if more blood or clots come out, this can indicate problems with the pregnancy, and the midwife or hospital should be called immediately. Accompanying cramps or pain in the uterus with a very bloody show are other signs that medical attention is necessary.
Points to note
Sometimes, a woman can see the mucous plug come away after certain activities. Intercourse can cause it to come out, especially when the due date is near, and a vaginal exam by a medical professional can also loosen it. In addition, many women are unsure about whether a discharge is the mucous plug coming out. A midwife or other medical professional can help to confirm the presence of a mucous plug if the woman shows them a sanitary pad with the mucous. Some women don't notice the plug coming out at all, which is completely normal.