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Cerclage pessaries

January 7, 2018

Do they make sense?

The cervix is a tube of fibrous tissue with an important job, to hold the baby in for nine months. If it fails the pregnancy ends in miscarriage or preterm birth.

Here’s how the cervix opens. The muscular upper part of the uterus contracts, effacing (shortening) the tube and then stretching the cervix passively over the baby’s head.

      

The cerclage pessary is a plastic device inserted in the vagina in such a way that it encircles that part of the cervix which protrudes into the vagina (picture below). The idea is that it can prevent miscarriage or premature birth by holding the cervix closed.  Trials have had mixed results (click here), but today I want to ask; is the idea even plausible?

Look at the pictures again, and get your head around the process of effacement.  How could a pessary lying loosely round that part of the cervix which protrudes into the vagina hold the cervix closed? The cervix can’t dilate until it has effaced.  But effacement pulls the cervix out of the pessary. The idea is impossible.

Even if the pessary exerted some pressure on the cervix it would not be able to do so on the very ones that most need it – those where the effacement/shortening has already started, or where the cervix was already shortened by previous surgery such as cone biopsy.

And don’t forget the pessary is a foreign body kept in the vagina for may weeks, sometime months. Infection is a well recognised cause of preterm birth. How did the idea that the cerclage pessary might work ever get traction?

Jim Thornton

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