Cervical incompetence. Most miscarriages occur in the first twelve weeks of pregnancy. Miscarriages at a later gestation are rarer, but still happen. If it does occur, the cause may be what is known as cervical incompetence, which affects about one in 1,000 pregnancies.
The cervix usually acts to hold the sac containing the foetus, until it is time to dilate and let it out (labour). If the cervix is weakened, it may open early and the pregnancy can, in effect, fall out. If this happens the dilation of the cervix is usually painless (unlike labour, in which much of the pain is from the cervix dilating).
If the cervix is prematurely dilating there may be spotting, or a sticky vaginal discharge, and possibly a watery discharge if the membranes of the sac rupture (‘waters breaking’).
Many women who have this condition are born with a tendency for a weakened cervix (congenital cervical incompetence). Others may have had damage to their cervix at some time which has affected its strength. Some examples of this include having had a very rapid labour and delivery, or delivery through a cervix which is not fully dilated. Another potential cause is damage to the cervix during a gynaecological procedure. The process of dilatation and curettage (D and C), used for abortions, gynaecological investigations, and after miscarriage, has long been thought to be a potential hazard for rhe cervix. More recent research has shown that with modem techniques, and experienced operators, the risk to the cervix from a routine procedure is minimal. Aggressive or rapid dilation, or dilation greater than that necessary for a twelve- to fourteen-week termination of pregnancy may carry more risk. Extensive cone biopsies of the cervix may increase the risk of cervical incompetence, but in most cases the amount of tissue taken does not interfere with the structure and function of the cervix.
If the problem is identified before a miscarriage has taken place, attempts may be made to treat a woman’s incompetent cervix. At between fourteen and twenty weeks, a non-dissolving stitch can be inserted into the cervix under general anaesthetic. This stitch can be cut when the pregnancy has progressed (after thirty-six weeks), and it is safer to go into labour.
Another, or additional, treatment is rest in bed, so that gravity has less of an effect on the contents of the uterus.
Success rates in the treatment of incompetent cervices vary with individual circumstances, but have been quoted as between 40 and 90 per cent.
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