My eldest son had IUGR - and was born full term 4llb - I have NEVER smoked, drunk or done drugs - I had the best diet of my life in pregnancy. Mine was due to high blood pressure and the placenta failing at the end of pregnancy (not picked up during pregnancy).
These things sometimes happen even if you have the best diet and healthiest life style - sometimes these things are just random. I lost my second son due to complications from PPROM (waters going at 20.6 weeks) I was under consultant care the whole pregnancy due to the IUGR the last time, NO ONE could have had a healthier more conservative life style than I did.. and yet I was one of the odd random staistics. Believe me I have gone over every second of my second pregnancy, looked for anything I did wrong.... got every medical opinon going and now 17 months on I can honestly say that I know in my heart of hearts it was a random medical thing that I had no control over.
I am sure it is the same as with the PPROM there are risk factors - but I fell into NONE of these categories. IT is probably the same with IUGR IUGA that they have to ask just incase you are in one of those groups - but it also will effect random people. You know what you have done and not in pregnancy and your conscience is clear - so please don't be made to feel bad when you KNOW you have nothing to feel bad for.
The fact that this problem has been identified, means they can hopefully put a care plan in place (if necessary) to help you and bubs. I know with this pregnancy I have extra growth scans to monitor my fluid, had fetal med scans to check the placenta, and the growth scans also look for signs of IUGR for bubs... but this time I have no signs of IUGR and am 39 weeks tomorrow.