MRPelvimetry for Breech Presentation

ABSTRACT & COMMENTARY

To determine the value of magnetic-resonance (mr) pelvimetry in the management of the breech presentation at term, van Loon and associates conducted a prospective study of 235 women randomly assigned to MR pelvimetry. The results were reported to the responsible obstetrician, the study group (n = 118), and a control group (n = 117), in which the pelvimetry results were not revealed until eight weeks after delivery. In the study group, decisions to allow a trial of labor or schedule an elective cesarean delivery were based on pelvimetry, while in the control group, these decisions were made based only on the available clinical information.

Patients were excluded for an estimated fetal weight of more than 4000 g, hyperextension of the fetal head, known fetal malformation, multiple gestation, a known pelvic or uterine abnormality, a previous history of cephalopelvic disproportion, and a planned elective cesarean delivery for indications other than a suspected pelvic contraction. In the study, acceptable values to determine if a vaginal breech delivery would be allowed included an obstetric conjugate of 11 cm or greater, a transverse pelvic inlet of 12.5 cm or greater, and an interspinal distance of 9.5 cm or greater. Oxytocin augmentation of labor was used if progress was poor. The primary outcome measurements were the rates of elective and emergency cesarean delivery and the condition of the neonate. Emergency cesarean delivery was defined as one performed after a trial of labor because of poor progress or because of non-reassuring fetal heart rate tracings.

Overall, the cesarean delivery rates did not differ between the study and control groups-42% vs. 50%, respectively. However, the emergency cesarean delivery rate was significantly lower in the study group than in the control population (19% vs. 35%). Thirty-five women were found to have abnormal pelvimetry-15 (13%) in the study group and 20 (17%) in the control group. The mean birth weights were not significantly different in the study or control groups (3307 g and 3286 g, respectively). However, the birth weights of infants who had a successful vaginal delivery were approximately 300 g lower than infants delivered by elective or emergency cesarean section in both groups. Neonatal outcome was excellent, although the Apgar scores of six infants in the control group who had a vaginal delivery despite abnormal MR pelvimetry were significantly lower than those of infants born vaginally to women with normal pelvimetry. One of these neonates had a transient brachial plexus palsy. Umbilical cord blood gas analyses were not performed.

Van Loon et al conclude that, while MR pelvimetry for breech presentation at term did not significantly reduce the overall cesarean delivery rate, it allowed better selection of the delivery route and a significantly lower emergency cesarean section rate without compromising neonatal outcome. (van Loon AJ, Lancet 1997;350:1799-1804.)

COMMENT BY STEVEN G. GABBE, MD

Cesarean delivery for the breech presentation at term contributes significantly to the cesarean section rate in the United States. Approximately one-third of all cesarean deliveries are performed for this indication. For most obstetricians and gynecologists, elective cesarean delivery is clearly favored as the route of delivery for primagravid and even multigravid women with a breech presentation at term. For many patients, there are clear indications of the need for a cesarean delivery, including hyperextension of the fetal head, a breech presentation other than a frank breech, and excessive fetal weight. Can pelvimetry, whether obtained with x-ray, CT scan, or MR be helpful in the decision-making process? The literature is controversial. Van Loon et al present an important study in which, for the first time, pelvimetry was obtained and the information was withheld for patients in the study group. As van Loon et al explain, because x-ray pelvimetry had never been used in the Netherlands for fear of the harmful effects of ionizing radiation on the fetus, they felt they could withhold the information obtained with MR pelvimetry. They observed that MR pelvimetry could be obtained quickly and easily and, in their center, at relatively low cost. These studies significantly reduced the rate of emergency cesarean delivery. Neonatal outcome was not affected.

As we attempt to lower the cesarean delivery rate in this country, we should reconsider our approach to breech delivery at term and carefully examine the data in this study. In many training programs, vaginal breech delivery is becoming a lost art, and our graduating residents do not feel comfortable performing this procedure in practice. Perhaps the wider use of CT or MR pelvimetry would allow better selection of patients for a safe vaginal breech delivery at term.