I have been pondering this recently! Ds2 has just turned 2, he was diagnosed IUGR, delivered at 38+5 weighing 4lb 15. It took him about 4 weeks to reach the very bottom of the 0.4th centile. He reached the 2nd centile at around 10 months and has stayed within it ever since. Btw, I'm not fixated on centiles (not bothered at all in fact), it's just useful for comparison in this case.
I was never given a reason/explanation for his IUGR and wonder now whether he was just small and was always going to be! At all my growth scans he had grown at a steady rate, just below the charts!
So I'm just interested in other people's experiences and whether you think your IUGR baby was actually just small and not growth restricted at all.