Babys size

So i have just finished at the hospital had to have an additional scan 31 +5days to check on the movement of my placenta. Great news that it has moved and they are happt for a natural delivery. However while they were dping the scan they dod measurements of baby head is all ok on track...legs all ok but babys tummy is on the small side they are a little concerned baby is not growing as big as they should be. 1.3kg at the moment. They will do more scans to monitor growth over the rest of the pregnancy just wondering if anyone else has been through this before.