What is the 38-week double-top diameter standard?

Biparietal diameter refers to the widest distance between the two sides of the fetal head, also known as the fetal head biparietal diameter. Usually pregnant women at 38 weeks of pregnancy, the standard value of biparietal diameter is 9.08 ± 0.59 cm. After 40 weeks of pregnancy, the standard value of the fetal biparietal diameter is 9.28 ± 0.50 cm.