I honestly don't know, but I had twins, so their being early is common, and the boy had intermittent cord-flow, and was growing more slowly than his sister.
They were born at 32 weeks, at 2lb7 and 3lb10, in SCBU for 3 weeks, trani care for a week, then home.
The one thing I wonder about is the fact I gained very little extra weight when I was pregnant apart from the babies, and after the birth was lighter than before I was pregnant. It certainly wasn't intentional, just a combination of bad morning sickness early on that lost me weight, and later I just tried to eat nutritious stuff, but didn't worry about calorie counts or anything. I certainly wasn't dieting, I just went by my appetite. No medical info ever suggested I should do anything else... but then after the birth, I read something suggesting that not eating enough in pregnancy can cause premature birth, and with twins, I should have been on something like 3000 calories a day.
So I feel guilty, but I'm not sure. Should I have force-fed myself eclairs?? God knows biscuits were a major food group for me anyway, I'm no health freak! Thankfully the babies are completely fine, but I do wonder if I could have avoided the prematurity.