Meb2--woohoo! 4cm is a lot! Hoping to read a birth story soon!!
Re: membranes' toughness, I've also read that a high caffeine intake will make the bag tougher. I swept my own membranes with my last two pregnancies multiple times. My 3rd babe was actually born in the caul (my attempted UC/43-weeker), and my last babe's water broke at like 9.5cm, just before I started pushing. Maybe i just have really thick bags of water, lol.