What is an incompetent cervix?

An incompetent cervix can lead to miscarriage or premature birth. What causes it?


The cervix, or neck of the womb, is an amazing structure.


During pregnancy, it is tightly closed, but with the onset of labour, it opens over a relatively short time to allow your baby to be born. This happens because contractions allow your cervix to dilate.

Cervical incompetence or weakness describes the situation whereby the cervix dilates without any contractions.

This results in either miscarriage during the middle trimester (12 to 24 weeks), or in your baby being born very prematurely.

What causes cervical incompetence?

Cervical weakness only happens if you have had an operation to remove part of your cervix (a cone biopsy), or where the cervix has had to be opened (for example for a termination).

But don’t panic: even if you have surgery or a termination, there is usually no increase in the risk of cervical weakness unless you have had multiple operations (more than three).

The cervix can also open without contractions if there is extra pressure, caused by too much fluid in the womb or a multiple pregnancy.

The normal pressure caused by your baby’s growth and movements will not cause the cervix to open.

An ultrasound scan at around 20 weeks can be offered to check that the cervix is closed. It is not done routinely, but is suggested for women with a medical or pregnancy history putting them at increased risk of cervical weakness.


If you have any concerns, consult your GP or midwife.


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