• Pelvimetry;
  • labor;
  • pelvic outlet;
  • dystocia

The influence of pelvic outlet capacity on labor and the efficiacy of routine low-dose radiological pelvimetry to anticipate dystocia during labor were studied pro-spectively among 1 429 unselected term primiparas, all having fetal head presentation and normal pregnancy. Outlet contraction was found in 0.9% and borderline outlet measurement in 5.3%. In 1 402 cases labor started spontaneously and 83 emergency cesarean sections were done. The incidence of cesarean section because of dystocia increased in inverse proportion to decreasing pelvic outlet capacity. The incidence of other emergency cesarean sections was not influenced by pelvic outlet size. In 79% of cesarean section interventions due to dystocia, pelvic outlet capacity was normal. Apgar score less than 7 at one minute was more commonly associated with a small pelvic outlet. Apgar score at 5 minutes and neonatal morbidity were not influenced by pelvic outlet size. Pelvic outlet capacity had a marked influence on the mode of delivery, but the practical value of radiological pelvimetry by fetal head presentation is rarely considered, except in very selected cases.