Cervical incompetence

As a pregnancy progresses, the pressure of the baby and amniotic fluid on such a weak cervix can cause it to dilate and cause a miscarriage. It is thought that up to 20 per cent of women who have recurrent miscarriages have, for a variety of reasons, a weak cervix. Once diagnosed, it is possible to insert a purse-string stitch into the cervix to keep it closed. This is sometimes called a Shirodkar suture.

Women who have this stitch need close monitoring immediately afterwards as the stimulation to the cervix can itself sometimes cause a miscarriage. But if everything is OK after about five days, the stitch stays in place until around the 38th and 39th week of pregnancy - or is removed straight away if labour starts before this time.