Whether the fetal biparietal diameter of 8.55cm is on the small side needs to refer to the specifics of the fetal gestational week, if it is less than the value of the corresponding gestational week, then it is on the small side, if it is within the corresponding gestational week, then it is normal. Fetal biparietal diameter reflects the size of the distance between the parietal bones of both sides of the fetus, the size of the biparietal diameter can be gradually increased with the growth and development of the fetus, generally speaking, the biparietal diameter of 8.55cm can be seen as early as 33 weeks of gestation, and can be seen as late as 37 weeks of gestation. Therefore, it is normal for the fetal biparietal diameter to be 8.55cm between the 33rd and 37th weeks of pregnancy, and if the size of the fetal biparietal diameter exceeds the 37th week of pregnancy, it is on the small side. When the size of the fetus is lower than the standard level of the same gestational week, you should consult a doctor to clarify the cause of the disease and rule out fetal malformations, so as not to lead to adverse pregnancy outcomes.