[Meaning of assimilation pelvis according to Kirchhoff in modern obstetrics]

To what extent is the cesarean section indication "arrest of labour" due to pathological forms of the pelvis and what is the meaning of the assimilation pelvis in modern obstetrics.

NMR-pelvimetries were performed in 166 post partum women from June 1993 to August 1995. The patients were divided into 4 groups. Group 1: patients who had had cesarean section owing to arrest of labour (n = 56), group 2: patients who had had cesarean section due to breech presentation (n = 20), group 3: patients who had had cesarean section owing to another indication (threatening fetal asphyxia, multiple pregnancy, premature delivery, placental abruption, gestosis, n = 40), group 4: patients who had a spontaneous delivery (control group, n = 50). After analysing the NMR pictures all the pelves were alloted to one of the case studies according to their pelvic form. The diagnosis "assimilation pelvis" was made according to the criteria of Kirchhoff (1949). The four groups were compared and analysed.

In group 1 an assimilation pelvis was found in 61%. The obstetrically most unfavourable canal pelvis occurred most frequently, amounting to 29%. In only 9% we found a contracted pelvis. In group 2 the proportion of the assimilation pelvis was even higher, rising to 65%. Only 35% of all pelves had a normal shape. In group 3 we found an assimilation pelvis in 50% of all cases. 66% of all patients with spontaneous delivery had a normal pelvis. An assimilation pelvis was found in 34%. In these cases duration of labour was prolonged by 4 hours on average (mean value: 9.5 hours).

Due to its frequency in our days the assimilation pelvis plays a major obstetrical role. This is true in particular when there is a pathological course of labour. From this results that pelvic parameters other than the conjugata vera will be of diagnostic importance, especially those parameters which are able to characterise the assimilation pelvis with its high promontory, the steepness of the pelvic inlet, the lengthening of the birth canal and the decrease of the hollow of the sacrum. We take the view that the angle of the pelvic inlet, the pelvic inclination and the direct length of the pelvis are of outstanding importance.