Small growth in femur length

Jellybean

Has anyone had this one their growth scans. Baby grown nicely in all areas in scans at 12w 20w and 28w but at 31 w just its fl has slowed down? It's still with in normal range but the length at 28 weeks was 54mm and at 31 its 55mm so its not really grown much? The doctor didn't seem too concerned afterwards because its still within normal range overall but I can help but keep thinking about it