And, it is often possible to do a pinprick rupture of membranes by holding the membranes between your fingers and tearing them slightly or pricking them with a pin and then continuing to hold them like this while letting the fluid drain out slowly. If you do these last two together, you can greatly reduce the likelihood of any possible prolapse. And I've never seen it done in the hospital. So, there's a little background on the prolapse issue. The mom's been in active labor for several hours and the baby isn't descending, apparently because of lots of fluid.
Birth is imminent.
There's some fear that babies born in the caul might aspirate the fluid after they're born. This is similar to the fear that babies will breathe in water at a waterbirth, although I've never seen any studies to indicate that either fear was well founded. Risks of artificial rupture of membranes include prolapse, risk of infection if vaginal exams are done after the membranes break, and increased stress on the baby. Most caregivers are bright enough to prevent prolapse, and some are smart enough not to rupture membranes until active labor is well established. However, there's not much you can do about the added stress on the baby.