In normal situations the cervix remains closed so that the fetus remains in the uterus and doesn't fall into the vagina. If the end of the cervix canal is open, it is described as an incompetent cervix. The most usual causes of such a condition are either late surgical termination of pregnancy (after 12 weeks) or cone biopsy of the cervix; both damage the muscle fibers that hold the cervix closed. This problem remains hidden until the first miscarriage occurs. The cervical canal starts to open around 14 weeks and at 20 weeks it is dilated to about 2.5cm (1 inch). There is usually a sudden loss of water, followed by a miscarriage with a little pain. A special stitch is inserted around the cervix to tighten it and is usually performed before or during the next pregnancy under a general anesthetic. This procedure is called a Shirodkar or purse string suture. it has a high success rate and most pregnancies proceed normally. Around 36-38 weeks the stitch is removed, with labor following shortly either naturally or through induction but some pregnancies do go to term.