The rate of successful vaginal delivery—when attempted—also differs markedly between the subgroups, from 68.3% in countries with high perinatal mortality to 44.7% in those with low perinatal mortality. Two reputable studies have determined the success rate of well-selected breech trials of labor to be around 70%.3,4 The 56.7% overall success rate in the Term Breech Trial raises questions about eligibility and selection criteria, and also about the variability in operator characteristics.
Another potential source of variability is the use of conduction analgesia in breech trials of labor. Normal, spontaneous progress in the first stage of labor, with optimal maternal expulsive forces and cooperation in the second stage of labor, is highly desirable for vaginal breech delivery. Inefficient maternal pushing in the second stage will expose the fetus to intravaginal manipulations that could jeopardize its well-being.
It appears that—at least in some cases—epidural analgesia has the potential to cause uterine hypocontractility and a prolonged, inefficient second stage of labor. For this reason, some skilled operators believe that epidural analgesia is best avoided in a breech trial of labor.5 We are not at all surprised that among the women in the Term Breech Trial who were able to deliver vaginally (in the group assigned to vaginal delivery), only 25.1% received epidural analgesia. What we do not understand is why a repeat analysis was performed after excluding the vaginal deliveries that did not involve epidural analgesia. Just the opposite might have been interesting: a repeat analysis after excluding the cases with epidural analgesia! Or, instead of an arbitrary stratification based on national PMR statistics—which might be totally irrelevant for the level of care in the particular institutions selected to participate in the study—stratification based on clinical factors such as the availability and use of epidural analgesia might have been more meaningful.
The selection process
The development of inclusion criteria was undoubtedly the first step in selecting appropriate candidates for the breech trial of labor. In practice, however, there is a second step in the selection process: the observation of labor abnormalities that might disqualify cases previously considered appropriate. In the Term Breech Trial, this second step was likely highly variable. For many experienced practitioners, conditions such as premature rupture of membranes (PROM), an absence of spontaneous labor, uterine hypocontractility, or an abnormal labor curve would prompt a reconsideration of the mode of delivery. Some experts believe that any arrest of spontaneous progress in labor necessitates cesarean section.6 Contrary to that, in the Term Breech Trial, as many as 22.4% of the cases assigned to planned vaginal birth had PROM, an unspecified number were induced, and a significant number of cases had augmented labor. Even Brenner, one of the few authors to conclude that the induction of labor is acceptable for women with breech presentations, noted that labor augmentation is associated with higher rates of infant mortality and morbidity.7
The authors conducted another repeat analysis after excluding 335 cases in which labor was induced or augmented, presentation was footling, or supervision was inadequate. These excluded cases, which account for 32% of the total for planned vaginal delivery, were responsible for 55.7% of the total adverse outcomes in that group only. This suggests that poor eligibility criteria may have contributed to an increased risk of fetal injury.
Does the trial reflect the customary clinical approach to breech presentation in labor or, rather, suggest that the operators felt bound by the randomized assignment? Is the higher rate of successful vaginal delivery in countries with high perinatal mortality indicative of greater operator experience with vaginal breech births (as speculated by the authors), or were the operators simply not as quick to resort to cesarean delivery, compared with their counterparts in countries with low perinatal mortality?
Interpreting outcomes
The authors’ interpretation of their results sometimes defies clinical plausibility. For example, in regard to the 16 cases of perinatal mortality, is it conceivable that the neonatal death from possible gastroenteritis in one infant who had been discharged home well, or the sudden infant death syndrome (SIDS) in a low-birth-weight infant also discharged home well, or the neonatal deaths from respiratory problems in possibly premature newborns might be attributed to something other than the mode of delivery? Also included are cases of intrapartum death with “fetal heart tones disappearing before a cesarean section could be done.” Such cases could reflect labor management rather than consequences attributable to mode of delivery.
We also are unconvinced by the authors’ contention that “the avoidance of labor…could have contributed to better outcomes.” The same logic could be extended to any woman in labor—whether presentation is cephalic or breech. An overall policy of planned cesarean section would prevent complications of labor because there would be no labor! Only 3 cases of perinatal death appear to be related to a difficult vaginal breech delivery in the group randomized to planned vaginal birth, equal to the rate of perinatal mortality in the planned-cesarean-delivery group.