A fetus with a biparietal diameter of 86mm is consistent with a 35+ week gestational age, and the size of the fetus weighs about 2600g, and its weight also needs to be estimated based on the femur length, abdominal circumference, and so on. According to the biparietal diameter of 86mm projected fetus in line with the 35 + weeks gestational age, 35 weeks gestation of the fetus 90% of the weight between 1974g ~ 3333g, so the projected fetal weight is about 2600g between. However, fetal weight varies greatly and is affected by nutritional factors, genetic factors and many other factors. In order to reduce the estimation error, it is also necessary to base on fetal femur length and abdominal circumference. There are many ways to estimate fetal weight, the common ones include estimation based on gestational age and gestational age (poor specificity and large error), estimation based on uterine height and abdominal circumference of the pregnant woman, and ultrasound estimation (based on fetal biparietal diameter, femur length, abdominal circumference, etc.), no matter which method of estimation is used, there are still errors, and obstetricians generally calculate based on multiple methods of estimation.