Ultrasound pregnancy detection is generally more accurate, but if the pregnant woman had irregular menstruation, diet and nutritional individual differences, ultrasound detection will be different from the clinical pregnancy weeks. The pregnancy time is counted from the first day of the last menstrual period, if the usual menstrual period is regular and there is no dietary and nutritional factors such as individual factors, ultrasound detection of fetal development should be consistent with the clinical pregnancy time, generally not too much error. In early pregnancy ultrasound measurement of the gestational sac, buds, head and hip length and other values, mid-late pregnancy ultrasound measurement of the biparietal diameter, femur length, head circumference, weight and other values, the software electronic system will be automatically based on the measurement of the data into the mathematical formula to arrive at the ultrasound equivalent of the gestational age, generally not much different from the age of gestation based on the last menstrual period. Due to the difference in the ovulation time of the pregnant woman’s own menstrual cycle, as well as diet and nutrition, the individual development speed of the fetus will also have differences, the b ultrasound projected pregnancy time will be with the clinical weeks of pregnancy there are errors.