A morphological study of the fetal ilium; focusing on the sexual differences of the greater sciatic notch

A number of studies on sexual differences in the ilium have been reported. However, most of these studies have focused on the adult ilium. With regard to sexual differences in the fetal ilium, few studies have been carried out. Especially, there have few studies regarding sexual differences in the fetal ilium using dry bones. In the present study, sexual differences in the morphological characteristics of the greater sciatic notch were investigated using dry fetal iliac bones. We examined 212 fetuses (106 males and 106 females) measuring 20.0 cm or more in fetal length with free of gross malformations or deformities which were collected at Saga Medical School. The iliac bones were excised from these fetuses and dried as materials for study. Fetal length was measured in the fully extended position and was classified into six groups each for males and females in 5-cm increments, giving a total of twelve groups. The inner lateral surface of the greater sciatic notch was magnified 25x using projector, traced, and the tracings were inputted to a computer (7600/120: Apple Co. Ltd) using a flatbed scanner. The width and height of the greater sciatic notch were measured, as well as the area of the greater sciatic notch. No sexual differences were noted regarding the increase in the width of the greater sciatic notch in fetuses up to 39.9 cm in fetal length. In fetuses measuring between 40.0 anf 44.9 cm, a significant sexual difference was observed, with the increase in greater sciatic notch width markedly greater in females. With respect to the increase in the height of the greater sciatic notch, no significant differences were noted. No significant differences were observed in the total area of the greater sciatic notch in fetuses up to 39.9 cm in fetal length. On the other hand, a significant sexual difference was observed in fetuses measuring 40.0 cm or more, with the total area markedly increased in females. In addition, no significant differences were found in the area between the two sides of the greater sciatic notch in fetuses up to 39.9 cm in fetal length, although significant differences were observed in fetuses measuring 40.0 cm or more. In female fetuses 40.0 cm or more in fetal length, the greater sciatic notch was found to be wider than in males, and the peak of the greater sciatic notch was displaced in the anteroinferior direction, farther from the auricular surface of the ilium and nearer the pubic bone. Thus these female fetuses show morphological characteristics of the adult female pelvic bone. Based on the results obtained, it is concluded that sexual differences can be identified in fetuses from the 8th month of pregnancy (fetal length 40.0 cm or more).