It is not normal for a fetus at 37 weeks to have a biparietal diameter of only 8.4cm. The average value of fetal biparietal diameter at 37 weeks is 9.23cm, due to individual differences in fetal growth and development, the size of the biparietal diameter within two standard deviations above and below the average is normal, so the normal range of fetal biparietal diameter size at 37 weeks is 8.63cm to 9.84cm, and the biparietal diameter of only 8.4cm is not within the range, which is generally not normal. Fetal 37 weeks biparietal diameter 8.4cm suggests that the size of the fetus is significantly lower than the normal range of the same gestation period, at this time you need to check whether the calculation of the gestational week is incorrect, and then further examination of whether there is intrauterine growth restriction and other conditions, so as not to affect the growth and development of the fetus. If there is abnormal development of the fetus, the next diagnosis and treatment plan should be guided by a professional physician, and the condition should not be neglected, so as not to lead to adverse pregnancy outcomes.