At 39 weeks of pregnancy, the fetal femur length is usually 7.34 ± 0.5 cm, and the value may vary due to individual differences, but should be within the normal range. If the examination reveals that the fetal femur is short or long, the range of abnormality is not large and there are no other developmental abnormalities, the fetus may be short or tall after birth due to parental genetic factors. Pregnant women can promote fetal bone development by strengthening nutrition and calcium supplementation, and have regular ultrasound to track fetal growth. If the fetal femur is normal, but the fetus is small or combined with organ malformations, it should be considered that the fetus has intrauterine development and growth restriction, and may have chromosomal abnormalities or other diseases, fetal chromosome karyotype analysis can be done, and after identifying the cause, the pregnant woman can choose to terminate the pregnancy early and treat the fetus after birth. The 39th week of pregnancy has entered the late stage of pregnancy, and the pregnant woman is likely to give birth at any time. It is important to observe the number of fetal movements, as well as whether there are paroxysmal pains in the abdomen and whether there is a large amount of fluid discharge or bloody discharge from the vagina. Usually pregnant women will go into labor 24-48 hours after seeing red, so it is important to seek medical attention and be prepared.