Blood work

Okay so if your baby was completely healthy and had TRIPLED their birthweight and meeting all milestones early but was staying in the 1st percentile - he actually wasn’t even on the charts at birth - would you let their doctor have labs done on them to check for a thyroid issue (keep in mind you would be holding your 7 mo old down to have their blood drawn for that) just because they weren’t “chunky and getting rolls”???? I’m really not interested in doing that because he shows NO signs of a problem...other than the fact that he’s small just like his dad was.