When giving birth, your healthcare provider will use the diameter of your cervix as an indicator for the birth process. The opening widens as a result of repeated contractions and pressure from the baby's head (or under if in the breech position).

Enlargement during pregnancy

As your cervix dilates during pregnancy, a mucus plug forms to close the opening. In the third trimester, your cervix may dilate up to 3 cm and the mucus plug may come out in one piece or as a thick discharge. You may not see it until your water comes. Dislocation of the mucus plug is caused by a combination of dilation and stretching or thinning of the cervix in preparation for birth. With this enlargement, which becomes more intense during birth, you may feel menstrual-like cramps.

Enlargement at birth

Expansion is important to give the baby an easier way to get out. Dilation until complete (10 cm) can take from a few hours to several days, and there is no way to predict how long the birth pains will last.

Starting the birth

If you're two weeks past your due date or if there's no contraction after the water comes in, your healthcare provider may recommend initiating birth. Other reasons for triggering birth include health risks for you or the baby, such as an infection in the womb, disruption of the placenta, or insufficient amniotic fluid surrounding the baby. Encouraging your cervix to dilate can be done manually by separating the amniotic sac from the cervix with a gloved finger or balloon-tipped catheter, or with medication.