Varied. The "bag of water" is actually 2 membranes: the amnion (inner sac) and chorion (outer sac). If the amnion breaks before delivery (but the chorion does not), the baby can become tangled in the fragments of the membrane and have structural defects, such as missing fingers or limbs, cleft lip, and constriction bands on limbs.
Kinda broad. A run down of disorder's is hard. Three can be "bands" in the sac that have potential problems; the bag can rupture causing problems; the "sac is two layers, the amnion and chorion that fuse at 16 weeks. I'm afraid your question is a bit broad and you may need to be a bit more specific. Good luck.