Fetal biparietal diameter of 5.5 centimeters at 23 weeks of gestation is normal. According to the Fetal Biparietal Diameter Standard Comparison Chart, the size of fetal biparietal diameter at 23 weeks of gestation is 5.80±0.44 centimeters, so the size of fetal biparietal diameter between 5.36~6.24 centimeters is normal. 5.5 centimeters is located in this range, and thus is normal. As the size of fetal biparietal diameter is affected by nutritional factors, genetic factors and the development of the fetus itself, its value can be large or small, but as long as it is within the normal range or the difference from the normal range is small, it is considered normal. There is no need to worry much and monitor closely. During pregnancy, you should pay attention to nutritional matching, so as to achieve balanced, scientific and reasonable nutrition, and you should have regular maternity checkups, and go to the hospital in time if any abnormality occurs.