The weight of a fetus with a biparietal diameter of 90mm is usually about 6 pounds, that is, 3,000 g. The formula for calculating the weight of a fetus through the biparietal diameter is Fetal Weight (g) = Biparietal Diameter (cm) x 900 – 5200, which is applicable to women who are more than 26 weeks pregnant. However, the weight calculated by the formula will have some error with the actual situation, and can only be used as a reference. Moreover, the weight of the fetus does not only depend on the biparietal diameter, but also depends on the length of the femur, the abdominal circumference, the head circumference and other factors, and there will be individual differences. There are individual differences between fetuses, some are fatter, some are thinner, but generally the weight of a fetus with a biparietal diameter of 90mm is considered normal if it weighs more than 2500g. If all other indicators are normal, it means that the fetus is developing normally, and you should pay attention to regular checkups. Fetal biparietal diameter is also known as the biparietal diameter of the fetal head, which is one of the factors determining whether or not the delivery can be successful, representing the widest distance between the left and right sides of the fetal head. During labor, you need to take into account the fetal biparietal diameter, the size of the opening of the uterus, the ability of contractions and the smoothness of the birth canal, etc. to decide whether to have a normal delivery or a cesarean section.