Fetal femur length is the length of the thigh bone, which is a common indicator used by doctors to observe the fetal development using ultrasound for pregnancy checkups. At 37 weeks of pregnancy, the normal value of fetal femur length is 7.10±0.52cm; at 38 weeks of pregnancy, the fetal femur length is 7.20±0.43cm; at 39 weeks of pregnancy, the fetal femur length is 7.34±0.53cm; at 40 weeks of pregnancy, the normal value of fetal femur length is 7.40±0.53cm, pregnant women can compare according to the normal data. If there is an abnormality is common in the following cases: 1, there is an error in the measurement: the measurement of femur length after 30 weeks of pregnancy allows an error of two weeks above and below, as long as it is within this range, pregnant women need not worry too much; 2, the fetal development is incomplete: if the femur length measurement differs greatly from the standard value, it is possible that the fetal development is incomplete. Pregnant women should do a good job of monitoring the health of their babies and themselves, if irregular abdominal pain, redness and other symptoms to go to the hospital for timely examination; 3, fetal congenital femur length is short: some fetuses due to genetic factors, resulting in congenital femur length is short, may have an impact on the height of the newborn, but this situation can be changed, now infants acquired nutrition has far exceeded the congenital impact, so wait for the fetus after birth, try to more Drink milk and take more calcium supplements, as well as strengthen physical exercise. In addition, pregnant women should pay attention to ensure adequate nutritional intake during pregnancy, such as protein, calcium, vitamins and trace elements to maintain normal fetal development, while controlling the intake of high-sugar or high-calorie substances to avoid over-nutrition, resulting in an oversized fetus.