Fig. 1. Drawings of true pelvic planes and positions of fetal head in each plane. (A) The human pelvis in coronal section, indicating the positions of the three pelvic planes: inlet, midplane and outlet. (B) The positions of the fetal head in each plane during labour. The dotted lines represent the true pelvic diameters more sexually dimorphic in each birth canal plane. (Reprinted with permission from Elsevier).