Question: how many cm dilated for water to break?
Answer: If your amniotic membrane ruptures -- or your "water breaks" -- the contractions may get much stronger. When the cervix dilates from 8 to 10 centimeters (called the Transition Phase), contractions are 2 to 3 minutes apart and last about 1 minute. You may feel pressure on your rectum and your backache may feel worse.