Fetal femur length of 52 millimeters at 30 weeks is normal. At 30 weeks the fetus has entered the perinatal period and the normal range for femur length is between 50 and 59 millimeters, with 52 millimeters falling slightly below the normal range. Femur length is the length of the legs of the fetus. Fetal femur length correlates well with maternal condition. When the numerical result is abnormal, it may be related to genetics, maternal malnutrition or overnutrition. Fetal femur length at 30 weeks generally refers to the results of ultrasound examination, which can measure the value of various fetal diameter items, but it is not 100% correct, and can be affected by factors such as clarity and the proficiency of the ultrasound doctor. At present, the reference value of fetal growth and development given by ultrasound is only an average value. During pregnancy, pay attention to a light diet, balanced nutrition, appropriate exercise and regular checkups.