Pelvimetry assesses the maternal bony pelvis before vaginal delivery, and one-view computed tomography (CT) , magnetic resonance (MR) imaging, or plain film radiography is suitable. Comparative data among these modalities for pelvimetry are lacking, but CT is favored due to its accuracy, low radiation dose, and widespread availability (homas, 1998). At Parkland Hospital, we use CT pelvimetry when possible to assess the critical dimensions of the pelvis (Chap. 2, p. 30). Although variable, some suggest specific measurements to permit a planned vaginal delivery: inlet anteroposterior diameter : 10.5 cm; inlet transverse diameter : 12.0 cm; and midpelvic interspinous distance : 10.0 cm (Azria, 2012; Vendittelli, 2006). Some have recommended maternalfetal biometry correlation. Appropriate values include: the sum of the inlet obstetrical conjugate minus the fetal BPD is : 15 mm; the inlet transverse diameter minus the BPD is :25 mm; and the midpelvis interspinous distance minus the BPD is :0 mm (Michel, 2011). With MR imaging, Hofmann and colleagues (2016) found vaginal delivery success rates of 79 percent in selected candidates if the interspinous distance exceeded 11 cm.
Currently, the American College of Obstetricians and Gynecologists (2016b) recommends that "the decision regarding the mode of delivery should depend on the experience of the health-care provider" and that "planned vaginal delivery of a term singleton breech fetus may be reasonable under hospitalspecific protocol guidelines." These guidelines have been echoed by other obstetrical organizations (Kotaska, 2009; Royal College of Obstetricians and Gynaecologists, 2006). Risks versus beneits are weighed and discussed with the patient. If possible, this is preferably done before admission. A diligent search is made for other complications, actual or anticipated, that might warrant cesarean delivery. Common circumstances are listed in Table
For a favorable outcome with any breech delivery, at the very minimum, the birth canal must be suiciently large to allow passage of the fetus without trauma. he cervix must be fully dilated, and if not, then a cesarean delivery nearly always is the more appropriate method of delivery if suspected fetal compromise develops.
TABLE 28-1 . Factors Favoring Cesarean Delivery of the Breech Fetus
Lack of operator experience
Patient request for cesarean delivery Large fetus: >3800 to 4000 g Apparently healthy and viable fetus either with active labor or with indicated delivery Severe fetal-growth restriction Fetal anomaly incompatible with vaginal delivery Prior perinatal death or neonatal birth trauma Incomplete or footling breech presentation Hyperextended head Pelvic contraction or unfavorable pelvic shape determined clinically or with pelvimetry Prior cesarean delivery
The conduct of both labor and delivery difer between cephalic and breech presentations. First, breech labor in general proceeds more slowly, but steady cervical progress is a positive indicator of adequate pelvic proportions (Lennox, 1998). Vaginal breech delivery is accomplished by one of three methods. With spontaneous breech delivery, the fetus is expelled entirely without any traction or manipulation other than support of the newborn. With partial breech extraction, the fetus is delivered spontaneously as far as the umbilicus, but the remainder of the body is delivered by provider traction and assisted maneuvers, with or without maternal expulsive eforts. With total breech extraction, the entire fetal body is extracted by the provider.