Pelvimetry revisited: Predicting cephalopelvic disproportion

Objective: To assess the clinical value of pelvimetry to predict dystocia due to cephalopelvic (cp) disproportion.

Materials and Methods: 50 patients who had received an abdominal CT scan postpartum between 01/2002 and 09/2007 were included in the analysis. Patients were divided into three groups by the course of birth: spontaneous vaginal delivery (A), dystocia due to cp disproportion (B) and patients who did not match either group (C). Various previously described methods used to diagnose cephalopelvic disproportion were evaluated in a blinded manner for their accuracy in diagnosing cp disproportion.

Results: Most pelvimetric parameters did not show significant differences between group A (n=7) and B (n=20) with obstetric conjugate, 11.8±0.5 vs. 12.0±1.2cm; interspinous distance, 10.8±0.7 vs. 10.6±0.6; intertuberous distance, 12.2±1.1 vs. 11.7±0.8cm; transverse diameter, 12.9±0.7 vs. 12.7±1.1 cm and sagittal outlet, 12.0±0.9 vs. 11.5±0.8 cm. The only significantly different parameter was the sagittal diameter at the level of the spinous processes (q) with 12.6±0.7 vs. 11.9±0.6 cm (p=0.0149, Mann-Whitney-U). The ROC analysis of the methods previously described to predict cp disproportion showed areas under the curve between 0.50 and 0.66. The determination of q alone offers a sensitivity of 90% with 63% specificity.

Conclusion: Pelvimetric dimensions in women with dystocia due to cp disproportion and those delivering vaginally do not show fundamental differences. The sagittal mid-pelvic diameter at the level of the spinous process (q) shows potential to detect disproportion with acceptable accuracy.

CT - cephalopelvic dysproportion - dystocia - pelvimetry