ADVANCES IN OBSTETRICS AND GYNECOLOGY

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The principal purpose of this obstetrical research is to work out the fundamental problems of the complicated mechanism of labor. Morphological analysis of pregnant women's pelves and fetal heads at term was made in view of labor progress by means of X-ray pelvicephalometry. Therein, the pelvis and the fetal head were comprehended in the identical scope in terms of size for the sake of comparison of them. Some new information was gained through this research concerning the interaction between the birth canal and the fetus during labor, which will be of great significance in predicting the prognosis of vaginal deliveries.
Following conclusions were attained from this comprehensive study:
(1) Value of prepartal X-ray pelvicephalometry
Prepartal X-ray pelvicephalometry is an extremely valuable weapon in the obstetric practice to evaluate cephalopelvic disproportion, to observe the prognosis of labor and also to predict fetal maturity.
(2) Importance of each pelvic strait
Pelvic inlet, midpelvis and pelvic outlet each have their own inherent factors respectively, which influence the labor process to a great extent. The pelvic dystocia due to the contraction of any of these three pelvic straits would effect a characteristic labor aberration. The labor abnormality caused by midpelvis contraction is the most distinct difficulty which occurrs not infrequently in nulliparous labors. Therefore, it should be asserted that the midpelvis plays not a less significant role especially in nulliparous labors than the pelvic inlet.
(3) Molding of bony birth canal
There exists an evident difference between the pelvic makeups of nulliparous women and those of parous women, which would account for the definite discrepancy in their labor mechanisms. In the course of labor the moldable pelvis of a parous woman can more easily yield and conform to the contours fit for a vaginal delivery than the rather rigid pelvis of a nulliparous woman. For this reason, the labors of parous women generally progress with much less difficulty than those of nulliparous women. Therefore, it should be advocated here that the molding of bony birth canal per se is one of the most essential factors influencing the entire event of a labor.
(4) Correlation of pelvic features to abnormal presentation
The fact that android pelvis is seen more commonly among breech presentations than among cephalic presentations suggests from a morphological point of view the necessity of a pelvic structural element to cause an abnormal presentation.

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