Influence of Pelvic Outlet Capacity on Labor: A prospective pelvimetry study of 1429 unselected primiparas

Abstract

The influence of pelvic outlet capacity on labor and the efficiency of routine low-dose radiological pelvimetry to anticipate dystocia during labor were studied prospectively 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.

Indications associated with increased cesarean section rates in a Swedish hospital

“…The reason is likely due to changes in practice in Sweden, where pelvic radiographs have almost disappeared. The decline of these examinations followed reports on their poor reproducibility, and poor predictability for the course of labor with cephalic presentation [13].…”

Pubic arch angle in prolonged second stage of labor: clinical significance

“…Cephalopelvic disproportion occurs when the pelvis does not accommodate for the passage of the fetal head, increasing the incidence of interventional delivery and the risk to both mother and infant 1,2 ; it is responsible for 8% of maternal deaths worldwide 3 . Floberg et al 4 reported a 0.9% incidence of contracted outlet among 1429 unselected term nulliparae, of whom 85% were delivered by Cesarean section (CS). The incidence of CS increased in proportion to decreasing pelvic outlet capacity.…”

Prolonged Labour Attributed to Large Fetus

“…Today the presence of inlet and outlet contracted pelvis is estimated to 0.15 and 0.9% respectively, although borderline outlet contracted pelvis is estimated to be about 5% [13]. Mean birth weight has been stable during the last decades.…”