What causes waters to break before active labour?

[daisy78]

My waters broke with my DS at 38w 1d. I didn't have any contractions so labour was induced 48 hours later to avoid the risk of infection.

I was wondering if anyone knows what could caused this? I don't smoke, and I have a very healthy diet. I did quite a bit of relatively heavy house work that day - could this have caused my waters to break?

I heard a posteriour baby could do this owing to added pressure in the wrong area. Don't know of any others though.