Generally speaking, the length of fetal femur at 39 weeks of pregnancy is 68.1-78.7mm, so the femur length of 71mm belongs to the normal range of values, indicating that the development of the fetus is good, no need to worry too much, and usually will not affect the normal delivery. Femur length, i.e. the length of the thigh bone, is one of the indicators of fetal growth and development, which can be accurately measured by ultrasound to reflect the length of the lower limbs of the fetus, and thus determine the development of the fetus. If the test shows abnormal femur development, it may be related to many factors, such as calcium deficiency during pregnancy, congenital heredity, intrauterine growth retardation and data error during measurement. If the measurement of the fetal femur length is significantly different from the standard value, it is necessary to improve the relevant examination under the guidance of the doctor to clarify the cause of abnormal fetal growth and development, so as to take targeted measures to deal with the problem. In addition, 39 weeks of pregnancy has entered the late stage of pregnancy, there is a possibility of labor at any time. Pregnant women need to monitor the fetal heartbeat, pay attention to the number of fetal movements, if there is a decrease in fetal movement or frequent fetal movement, should consider whether there is fetal hypoxia. In addition, pay attention to a balanced diet, replenish the nutrition needed by the fetus, exercise appropriately, and keep a happy mood. If there are symptoms such as irregular abdominal pain and redness, it suggests that labor may be imminent, and you should be admitted to the hospital to wait for delivery.