Clinical assessment of the pelvic cavity and outlet.

A clinical assessment of the pelvic midplane (or cavity) and the pelvic outlet was made in 1,286 singleton pregnancies with a cephalic presentation of the fetus. 43 cases (3.4%) of pelvic contraction were excluded. The mothers were divided into two groups: those with an adequate pelvis and those with a borderline pelvis (18.6%). Those with a borderline pelvis were further subdivided into three categories: those with a borderline outlet, those with a borderline midplane and those with a borderline midplane and outlet. With a funnel pelvis the incidence of occiput posterior positions and vacuum extractions was three times as high and the duration of the first and the second stages of labor slightly longer when compared with those who had a normal pelvis. A borderline midplane seemed least harmful type with lower incidences of caesarean section and vacuum extraction, and a first stage of normal duration. Although birthweight had an effect on the duration of the first stage of labor in women with an ample pelvis, this was not the case with a borderline pelvis. The assessment of fetal weight therefore seems unnecessary in with a borderline midplane or outlet. With a borderline midpelvis and outlet the course of labor seemed normal in most cases. Clinical assessment of the midpelvis and the pelvic outlet seems to be the best method of measuring pelvic capacity.