Understanding Water Breaking: Causes, Symptoms & What to Expect

Question
How does your water bag pop? Is it the baby that pops it? Or does it do it on its own some how? and if so how does that work?

Answer
The amniotic sac is a bit like a water balloon.  It will break under pressure without support, it will break if it is meddled with too much, and sometimes it's hard to tell exactly what makes it break.  Usually, the water breaks naturally sometime during active labor, between 5 cm dilation and the onset of pushing.  About 5-15% of women will experience their water breaking prior to the onset of labor, and an even lower percentage of babies will be born "in the caul" with an intact amniotic sac at the time the head is born.  Sometimes, the water can break after a care provider does an internal exam and/or strips or sweeps the membranes; the manipulation of the sac during the exam can cause the breakage.  Other times, there's just no way to know why it breaks when it does.  Usually, though, it breaks under pressure of contractions after the cervix has dilated enough to no longer provide support.