A damaged cervix means that it cannot hold the weight of the pregnancy. In some cases, the cervix opens up with no contractions or pain and even opens completely. The dilation causes the amniotic membranes to bulge through the opening and eventually tear, often before the baby can survive outside the uterus. This irritates the uterus and brings on pre-term labor. In many cases, labor is detected when it is too far advanced and is usually irreversible.
Attribution: Avallain