Quoting G[PLM]:" I know I am being a worry worm but.... My water broke with my 2nd at 28 weeks and I delivered within ... [snip!] ... this (prolapse) if your water breaks before term? I know I know, I need to stop worrying but I can't, I think its the hormones."
It's more common if you're early, and it's more common if you're water is broken. If your water breaks you're supposed to try NOT to walk around because the idea is that the baby is small, so the cord can slip around the baby where as if it were larger and in place it would be fine.
Realistically, it's uncommon to go into labor that early, even less common to actually have your water break, and then the odds of having a cord prolapse are even smaller.
I'd try not to worry.