The magnetic resonance imaging-based fetal-pelvic index: a pilot study in the community hospital

This study was undertaken to assess feasibility of magnetic resonance imaging (MRI) pelvimetry in conjunction with fetal ultrasonography as a technique in evaluating patients with previous cesarean sections for cephalopelvic disproportion (CPD).

Pregnant patients with one previous cesarean section for CPD who planned a trial of labor after cesarean (TOLAC) were recruited to undergo MRI pelvimetry and fetal ultrasonography at 37 to 38 weeks. Entry criteria included no previous successful vaginal deliveries and no contraindications for vaginal delivery in the ongoing pregnancy. A fetal-pelvic index was calculated for each patient but not disclosed to patients or their physicians. The pregnancies were managed routinely. Analysis after delivery was used to ascertain whether this index would have predicted clinical outcome.

There were no difficulties in performing the MRI or ultrasound. Sixteen patients completed their pregnancies. Three patients did not labor. The fetal-pelvic index was plotted on a scattergram and compared with the outcome. Three discriminatory zones were identified. Five of 6 patients in the most favorable zone delivered successfully. Two patients in the most unfavorable zone had failed vaginal birth after cesarean section (VBAC) attempts. In the 5 patients in the middle intermediate zone, TOLAC success appeared to depend on fetal presentation and gestational age.

The use of comparative MRI pelvimetry and fetal ultrasonography is feasible in a community hospital. In this pilot study, it appeared to have potential in enhancing the management of VBAC candidates. This technique may allow sorting of patients before labor into zones that would favor or preclude VBAC attempts.