Small baby with GD

So I was diagnosed with GD at 8 weeks and have been on insulin since 12. My numbers have been pretty stable since being on the insulin. I had my anatomy scan at 22 weeks and baby boy was measuring in the 68th percentile. Today I had a growth check at 28 weeks and he was measuring in the 16th percentile. I feel like that’s a big drop to happen in such a fast time. The doctor didn’t really say anything about it, but has this happened to anyone else? Regardless of having GD or not?