Three-Dimensional Fetal Head

TERRY J. DUBOSE, MS, RDMS, The fetal head is three dimensional (3D). As 3D sonography becomes a clinical reality, there is a need to describe standard biometric parameters by which the head shape, proportions, and volumes may be measured and analyzed. This particular study presents measurements and methods that are applicable to newer 3D imaging systems. These measurements will provide consistent methods for evaluating the size, shape, and proportions of the fetal skull using orthogonal planes. In this research, three diameters of the fetal skull were measured and analyzed using standard real-time sonographic equipment. The biparietal diameter (BPD) measurements and the three diameters’ averages (3D BPD) were compared using a t test of paired two-sample means; no significant difference was found (p = .497, r = 0.996). The 3D BPD is equal to the normal BPD, that is, (FOD + BPD + VCD)/3 = BPD. The 3D BPD can be used in any regression or nomogram in place of the BPD to correct for head shape and molding.