If your water (aka "amniotic sac," "bag of waters" or "membranes") hasn't broken on its own when you arrive at the hospital, and you're five or more centimeters dilated, your OB might recommend bursting the bag by hand—especially if your cervix seems to be making slow (or no) progress. (Some OBs will go ahead and break your water at 3 or 4 centimeters.)
The reasoning behind this: "Artificial rupture of membranes" (popping a hole in the amniotic sac) will usually jumpstart labor by getting serious contractions underway. If labor is moving along fine, you and your doctor might decide to wait this one out—after all, contractions tend to be more painful after your water breaks. If the OB doesn't rupture your membranes, the sac will probably break on its own during labor, though once in a while it stays intact until baby makes an exit. (Either way is fine.)
To break your water, the doctor will reach up and prod it with something that looks like a crochet hook. You might feel (very little) discomfort as the device enters your vagina, but as for the actual water breaking, most women only feel a big, warm gush of liquid.
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