I just googled it after the dr suggested that's what i had and it was spot on for me. I found story after story that matched by situation. Irritable uterus is just one thing that causes premature labour, for you it could be anything. With the irritable uterus you can have stacks of braxton hicks close together for long periods of time throughout your pregnancy and usually they don't make you start dilating but occasionally like in my case sometimes they do. I had tightenings from 12 weeks. My bh are now constant and often painful but they aren't making me dilate. It's a tricky thing to have because you never know when its BH or the real thing which is why i ended up with prems. I was 4cm+ and just having a lot of painless BH when i had both my boys. This time around i've had painful BH for 2 and a half weeks so far after painless bh from 12 weeks. Lots of people with IU go to full term though so it's a confusing thing to have. If any of this is familiar to you than you should speak to your dr/midwife because there are things you can do to get as far as possible ie. bedrest, no sex etc