..it could mean a few things!
Sometimes babies measure small because..
- they are not gaining enough weight via eating.. meaning perhaps they aren't getting as much as a Mom thinks while breastfeeding, this is pretty common.. especially in first time Moms
- they in some instances are burning more calories than taking in.. thus, supplementing might have to occur to catch them up
- they sometimes are built tiny and petite (genetics).. just like people :) doctors typically want to establish that a baby CAN gain weight and then it's easier to see if how they gain weight they stay small and petite or grow grow grow!