Magnetic resonance–based serial pelvimetry: Do maternal pelvic dimensions change during pregnancy?

The purpose of the study was to evaluate the stability of the maternal pelvis over the course of the third trimester and the puerperium. Pregnant patients were recruited to undergo comparative magnetic resonance–based pelvimetry and fetal ultrasonography at 37 to 38 weeks of gestation. Most of the patients were recruited from a study of women who planned a trial of labor after a previous cesarean delivery for cephalopelvic disproportion. These results have been reported previously. Patients then underwent magnetic resonance–based pelvimetry within 3 days and at 3 months after delivery. Postdelivery analysis was used to answer the question: Do pelvic dimensions change after delivery? Eighteen patients completed the study. Eleven of the patients underwent cesarean deliveries, of which 4 deliveries were before labor. Seven patients had successful vaginal births after their previous cesarean delivery. Statistical analysis of the 18 patients determined that pelvic measurements did not demonstrate change over the course the study. Serial magnetic resonance–based pelvimetry showed relative stability of pelvic measurements through the course of pregnancy and delivery. If comparative pelvimetry is to be useful as an antepartum predictor of labor success, then it may be possible to obtain reliable pelvimetry in those patients anytime after delivery.