Hi
I've had two IUGR babies. One was stillborn at 38 weeks & my second was born by section at 37+4 because of the first. Both were IUGR but not medically (long babies & mere grams over the threshold but looked very very thin both of them).
I discovered after my second I had a double uterus so half the space to grow.... along with other clotting question marks over my placenta development.
Anyway, my second was at the 3rd centile once born. He was 5lb 15 so not tiny but v skinny if you held him or looked at him. He too had jaundice but not too bad he only had to be readmitted for 36 hours of phototherapy.
Docs & HV had no concerns because he was a) early so explaind birth weight & b) he wasn't under the 2500g weight to be medically IUGR despite my protestations....
HVs did however over the coming months have an issue with his development as his chart wasn't matching the expecting climb for a baby. He was jumping centiles each week.... He is now 61st centile with 98th centile head circ. at 10 months. HV were at 6 month mark telling me to withhold food as he was growing too much (I ignored this advice!!!!!).
Don't worry yourself. I was very worried about it & he has grown so much in spite of it! He started BF & after a phase of dodgy green poop I decided he was IUGR & trial & error method of latching could cause him to stop growing so well so to give FF. My personal decision & best one, aside from opting for a section, I have ever made.
As a side note, he saw my obstetrician when he was 6 months old & he was dumbfounded at how well he had grown given how small he was at birth proving in my mind he WAS IUGR & just needed the opportunity to thrive.
Oh & he slept through from 9 weeks & is an amazing little eater. He's always loved his food & I half think that was because in utero he was left hungry.