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Why does the cervix form a mucus plug during pregnancy?
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prenatal development
An ultrasound image of a human fetus.
During pregnancy, the cervix produces a significantly thickened mucus within the endocervical canal. This mucus forms a protective plug that serves a vital physiological function: it seals off the uterus from the external environment, acting as a barrier to help prevent infection from reaching the developing fetus.1
As the body prepares for parturition, this mucus plug thins and the cervical walls relax to facilitate the delivery process.1