Three Dimensional Fetal Head
Click here for full coronal head image.
3D BPD Correction
Molded Fetal Heads
Click here for molded head images.
The problem of head molding as it relates to the accuracy BiParietal Diameter (BPD) of the fetal head has long been recognized. The tendency of this single linear diameter of the head to vary with molding and head shape is the reason that the Head Circum
ference (HC) is so widely used. However, the HC is subject to the same molding as is a single diameter because the HC does not account for the third dimension of the skull, the vertical cranial diameter (VCD). The VCD was first published in 1985 (DuBose
T. FETAL BIOMETRY: Vertical Calvarial Diameter and Calvarial Volume. J Diag. Med. Sonography; 1985; 1(5) 205-217). In 1986 the Society of Diagnostic Medical Sonographers (SDMS) recognized the research by the presentation of the Kenneth Gottesfeld Award
Additional research found that the 3D BPD is much simpler to calculate than the Cranial Volume (CV). It turns out that the 3D average (BPD + FOD + VCD)/3 is equal to the BPD on normal charts. Therefore, the 3D BPD Correction can be used to estimate feta
l age from a standard BPD chart or substituted in any regression using the BPD to estimate fetal weight, age or size. The 3D BPD will result in more accurate estimations. If you do not have access to the older JDMS then you may find instructions for me
asuring the VCD in DuBose T. FETAL SONOGRAPHY; W. B. Saunders Co., Philadelphia, 1985, Chapter 8, Cranial Biometry; or in Berman MC. Obstetrics & Gynecology: Diagnostic Medical Sonography Volume I; J. B. Lippincott Co., Philadelphia, 1991; p
- 3D BPD Correction = (BPD + FOD + VCD)/3
- where FOD = frontal occipital diameter, VCD = vertical cranial diameter
- also, 3D BPD Regression = -58.5 + 5.965(AA) - 0.0564(AA2) + 175.4/AA
- where AA = Average Age of multiple fetal parameters in equivalent LMP weeks.
The VCD is the height of an imaginary triangle in the coronal view of the fetal head. The triangle has as its base an imaginary line, the hippocampal base line (HBL), which is tangential to the bases of the echogenic circles around the bilateral hipp
ocampal gyri. This measurement is much easier to obtain than it at first appears. Click on the 3D BPD Correction at the top of this page to see a version of the coronal view and VCD measurements (the colors are false, my machine doesn't really do this
kind of color).
By calculating the diameter of the circle which circumscribes a new parameter (TriCD) is derived which, theoretically, is also equal to the BPD in normally shaped heads. This gives us at least three calculations that are normally equal to the BPD:
BPD = 3D BPD Correction = TriCD = 3D BPD Regression
3D Head Growth Curves.
3D Head Growth Curve Residuals.