The main method for the early screening of the developmental dysplasia of the hip (DDH) is the ultrasound imaging. There are several studies about the ultrasound imaging of newborns' hips, but only a few studies include the prenatal period of life. Our aim was to examine the prenatal development of the hip joint through the evolution of the a angle seen on the ultrasound, described in the Graf R method, combined with anatomical dissection. Materials and Methods: Thirty-one post-mortem fetal hips were analyzed trough anatomical dissection, in 25 cases trough ultrasound imaging, in which the a angle was measured. Based on the morphometric examination, we applied the sine rule and we calculated the alpha 1 angle, which also represents the coverage of the femoral head. Results: Based on the morphometric examination, not only the diameters of the femoral head and of the acetabulum, but also the joint cavity (X) showed an increase during development. Both of the a angles (measured a, calculated alpha 1) showed a decrease as the fetus developed. Conclusions: The decrease of the angles (alpha, alpha 1) and the increase of the joint cavity during development correspond to the findings of the main research papers: the hip joint is less stable in the perinatal life. The a angle can be accurately determined only after the ossification of the acetabulum had started, in our case after the fetus is older than 18 weeks.