Cervical incompetence is the weakening or abnormal opening of the cervix early in pregnancy. The cervix is the entrance to the uterus. A loose cervix often leads to dilatation of the entire cervical canal during the second trimester. The uterine lining that holds the fetus in place (the sac) may rupture and the baby may be born prematurely. Up to 2% of all pregnancies may be affected. This condition can cause 20% to 25% of all second-trimester pregnancy losses.