When I was 23 weeks pregnant I went into pre term labour with my DS. Thankfully my Dr stopped the labour and I went on to have him at 42 weeks.

I asked for answers why and she didn't have any other than to slow down and take it a little easier. I had been travelling alot with work and doing 12 hour days.

I was careful with pregnancy number 2 and had Paisley at 41 weeks.

Sorry I don't have any answers for you. Just my experience.