It is true that the fetal weight can be measured based on the biparietal diameter, but the results of this method are somewhat different from the actual weight of the fetus and are not completely accurate. The formula for calculating the weight based on the fetal biparietal diameter is: multiply the biparietal diameter by 900 and subtract 5200, in grams. However, this method can only estimate the fetal weight and there is some error. Other methods can be used to calculate fetal weight in the middle and late stages of pregnancy, based on a comprehensive assessment of fetal biparietal diameter, femoral length, chest circumference, abdominal circumference and head circumference together. In clinical practice, the fetal weight can also be estimated by combining the maternal uterine height and abdominal circumference, and the fetal weight can also be projected based on the length of the femur, but the fetal weight can only be accurately measured after delivery, and it is mainly based on the weight of the fetus after delivery. The weight measured by whatever method during pregnancy is only used as a reference that can help the doctor to assess the mode of delivery of the pregnant woman. During pregnancy, it is recommended to increase nutrition, work and rest regularly, avoid overexertion, stay away from toxic and harmful chemicals and environments, and forbid sex as much as possible during the late pregnancy to avoid stimulating contractions that may lead to early delivery. Seek medical attention if you feel unwell.