Hi Doc, I Am 28 Weeks Pregnant My Baby Weight

Hi doc, I am 28 weeks pregnant my baby weight is 2.5 pound my doc says it is normal and didn't give any supplement but in my relatives their are some cases in which fetus stops growing in 7 month of pregnancy and is 4 pounds which shows in 7 month baby should have 4 pounds there are several cases in my relative that baby have 4 pounds in 7 month of pregnancy and on the time of delivery baby is of 6 pound which is so called a healthy baby I am also 7 month pregnant but my baby weight is 2.5 pound please help weather is should worry about it or not