How is biparietal diameter (BPD) measured?

Biparietal diameter (BPD) is a key measurement used in obstetrics to assess fetal growth and development. It is specifically measured at the level of the thalami and cavum septi pellucidi. This location is precisely chosen because it provides a consistent landmark that can be reliably used in sonographic imaging to capture the transverse view of the fetal skull.

When assessing BPD, the measurement is taken from the outer edge of one parietal bone to the outer edge of the opposite parietal bone. By utilizing the thalami and the cavum septi pellucidi as reference points, the measurement reflects the widest diameter of the fetal head, which is crucial for estimating gestational age and identifying potential complications related to fetal growth.