Abstract: Last menstrual period（LMP），which is a common means of estimation of gestational age，is simple，economical and low-cost. However，this method has many defects. Studies have demonstrated ultrasonography measurement to be superior to the LMP in estimation of gestational age and is receiving more and more attention. It is becoming the preferred choice for estimation of day of delivery in many countries. There is clinically significant difference among areas when determining gestational age on the basis of ultrasonography measurement. But there is no a sonographic dating formula based on ultrasonography measurement in Chinese population. This paper reviews the LMP and ultrasound characteristics and calculate gestational age ultrasound assessment of gestational age specific method for processing to provide a better basis for obstetrics.

Key words: Menstruation, Ultrasonography, Gestational age, Pregnancy