At 28 weeks, a fetal femur length (FL) measurement of 48mm is within the normal range for baby growth. The average FL at this stage is around 47-54mm, so your baby's FL falls within that range. It's important to note that these measurements are just estimates and can vary slightly. As long as there are no other concerning factors or abnormalities detected during your prenatal check-ups, there is no need to worry about your baby's growth. Your healthcare provider will continue to monitor your baby's development and address any concerns if necessary.