BPD is the biparietal diameter, which is the largest transverse diameter of the fetal head and averages 9.3 cm at full term. BPD is the biparietal diameter, which is the distance between the two parietal eminences, and is the largest transverse diameter of the fetal head. It is an important indicator for determining fetal development after 16 weeks of pregnancy, and should also be combined with abdominal circumference and femur length to comprehensively assess fetal development at different gestational weeks. When the ultrasound examination suggests that the biparietal diameter is small or large and other abnormalities, but also follow the doctor’s instructions to do a magnetic resonance imaging to rule out the possibility of developmental abnormalities. During pregnancy, you should ensure reasonable and balanced nutrition under the guidance of your doctor, and maintain an appropriate amount of physical exercise to maintain appropriate weight gain during pregnancy, so as to avoid over-eating or irrational diets that may make the fetus grow too large or too small, which may increase the risk of pregnancy and delivery. During pregnancy, you should also follow the doctor’s instructions and undergo obstetrical examination on time, so that abnormalities in the development of the fetus can be detected and dealt with at an early stage.