The standard value of femur length at 23 weeks of pregnancy is 4.21±0.41cm. femur length is one of the important indicators for observing fetal growth and development, if it is within the normal range, pay attention to regular monitoring, but some pregnant women find that the femur is long or short during the monitoring process, the details are as follows: 1. femur is long: it may be related to genetic factors, measurement errors, fetal growth and development abnormalities, etc., if If the femur is simply long, there is usually no big problem, pay attention to regular review and dynamic observation; 2, short femur: calcium deficiency, genetic factors, intrauterine growth retardation, fetal chromosomal abnormalities, etc. may lead to short femur, in addition, there may also be measurement errors, if it is the first time found, first of all, to check the week of pregnancy, followed by a comprehensive analysis of other growth indicators, some pregnant women are irregular menstruation, late conception time, may be the result of the short femur. Some pregnant women have irregular menstruation and late conception, which may be due to the inconsistency of the gestational week. At the same time, we should pay attention to nutrition and calcium supplementation, and review the ultrasound at an interval of 1-2 weeks to observe the growth and development of the fetus.