I find that a woman at 3cm looking like she is about to birth needs lots of attention because, either, she *is* gonna birth any minute, or she has a really bad malposition and she might need some help getting that baby moved around to a better position before the baby gets too far wedged in that position. Y'know?
I had a mom this week go from 4cm/70% effaced to fully in just a few minutes. That baby would have flown out, except he had his arm wrapped around his chest and up by his ear. We wondered why this 4th time mom was pushing so hard and worried about shoulders. Well this chunky almost 9 pounder just had the arm wrapped around and a little nuchal hand by his ear that slowed him down. Her last labour was under an hour, too, beginning to end.
I've also had 2 multips stalled at 7cm for a loooooong time and the baby come out with my fingers immediately after an AROM. It was like, "ok, lovely clear fluid... and a baby! Hello little one!"
My all-time fasted client carried equipment around with her as she reported her last baby was born with only a couple of contractions. She carried a little kit around at work and around with her on the farm she lived on. One night I got a page from her with no message. I waited a bit while I tried to unsuccessfully contact her then headed out to her place. When I arrived, she was in the tub, placenta in a bowl, and the baby dressed and in a car seat watching her bathe. Her 5 other kids were asleep in her room. It was 4 am. She said she tried to get me there, but awoke with a contraction, paged me, then on the next contraction the baby slid out, with her not moving from the side of the bed! She said it was so fast that none of the kids, not even the ones bedsharing, woke up. Sure enough there was her barely mussed sheets, sleeping kids in the room, and a little tiny smear of blood on the side of the bed and a bit on the floor. She clamped the cord and cut it herself, then gave herself a bath, and dressed the baby, all in the 30 minutes it took me to get there. I had very little to offer her, other than cleaning that littlle bit of blood up, and playing with the kids. She was awesome and and inspiration. (She was also interesting because, even at about 110 lbs, she never had a fundal height above 26 (!) at term, and had 8lb+ babies! She hardly looked pregnant! I still can't figure out where she hid those babies from a pure physical perspective - she was stick-thin. She had such great faith in her body and was a lot of fun to care for.) When I think of truly precipitous birth, I think of her.