28 weeks pregnant, head circumference and femur length difference of three weeks may be a normal phenomenon, or may be anomalous phenomenon, need to be specifically analyzed. 28 weeks pregnant, head circumference and femur length difference of three weeks, first of all need to verify the gestational week, to exclude the gestational week calculation error, need to improve some other checks, such as biparietal diameter, abdominal circumference, etc. to make a rough prediction of fetal weight, if the fetal head circumference and femur length are in the normal range, the general impact is not great, regular obstetric examination can be. If the fetal head circumference or femur length is not in the normal range, lower than the lower limit value or higher than the upper limit value, need to comprehensively analyze whether there is intracranial hydrops, long bone dysplasia and other diseases, and at the same time, dynamic monitoring of the development of its indicators, and, if necessary, to carry out prenatal diagnosis, to exclude fetal chromosomal abnormalities. Pregnant women with a large head circumference and a three-week difference in femur length in the 28th week of pregnancy need to be comprehensively analyzed, improve the relevant examinations, and under the guidance of the doctor to carry out standardized examinations or treatments.