Strengths and limitations
The strength of the study is the thorough review of the medical records, done independently by four obstetricians. A particular strength is that two examiners were not informed of the outcome when they reviewed and assessed the course of the deliveries.
The low number of deliveries is a limitation. Thus, lack of statistical significance between case and control deliveries must be interpreted with caution. Nonetheless, the percentages of most risk factors for adverse outcome of vaginal delivery were similar in the two groups. Moreover, statistically significant differences between the groups regarding suboptimal care or indicators of difficult deliveries (i.e. use of Pipers forceps and breech extraction) should also be interpreted with caution.
The review of the hospital records revealed that two case deliveries were misclassified as breech deliveries by the MBRN, while the children were in fact born in cephalic presentation. Correspondingly, children who were in fact born in breech may have been misclassified in the MBRN as being born in cephalic presentation. Thus, we may have missed one or more breech deliveries with suboptimal care or where the delivery was not in accordance with the Norwegian guidelines.
Comparison with other studies
In a comparable study of term breech deliveries during 1982–92 in Denmark Krebs et al. studied the deliveries of 12 singletons without congenital anomalies who died intrapartum, or during the first week of life, and 23 controls. The authors reported that seven deaths (58%) were potentially avoidable [
16] and that antenatal and/or intrapartum care was suboptimal in both in case (42%) and control (30%) deliveries. Regarding potentially avoidable deaths and deaths associated with suboptimal care, their results are in line with the findings of the present study. However, the proportion with suboptimal care in the control group was much lower in our (7%) than in the study in Denmark (30%). This difference may be explained by general overall improvements in both antenatal and intrapartum care between 1982 and 92 and 1999–2015.
Female fetuses are more likely than male fetuses to be in breech presentation at birth [
17] and in line with this, there were more girls than boys in our control group. However, in the case group, two out of three infants were boys. Although not statistically significant, the differences in sex distribution between the case and control deliveries may be in line with studies showing that boys in general are more vulnerable than girls to fetal distress during labour [
18,
19]. Another possible explanation for the predominance of boys in the case group is that boys have higher weight and head circumference than girls [
20], which could explain why boys are more prone to complications during breech delivery. We are not aware that other studies have reported that the outcome of breech delivery may be different in boys and girls.
The proportion of fetuses in breech presentation undiagnosed before labour was slightly higher (30%) in our study than in other European studies (17–28%) [
21,
22]. When breech presentation is discovered in labour it may be too late to evaluate the maternal pelvis and the fetal size, and external cephalic version may no longer be possible. However, studies published prior to the TBT did not find higher mortality or morbidity in deliveries of undiagnosed breech presentation, compared to those diagnosed before labour [
23,
24]. Since it is likely that obstetricians at that time were more experienced in the management of vaginal breech deliveries, it may be a concern that as planned CD increases as the preferred mode of delivery, deliveries where breech presentation is diagnosed late in labour, may be managed suboptimally.
Interpretation
Despite the fact that all deliveries were in line with Norwegian guidelines, 12 in-hospital deaths were potentially avoidable had CD been planned and performed. In eight of these cases, an unexpected complication occurred during delivery. Sudden, unexpected events also occur in deliveries in cephalic presentation and is a potential, albeit rare, complication of any vaginal delivery. However, in our population, seven of the eight sentinel events were events that occur more commonly (cord prolapse) or typically (difficult delivery of the head) for vaginal breech deliveries.
Intrapartum care was considered suboptimal in six of the potentially avoidable deaths. In all six cases, fetal heart rate had been misinterpreted. Suboptimal intrapartum care was more common in case than in control deliveries, and therefore the results of this audit may suggest that better training in the interpretation of fetal heart rate could have improved survival.
Although it was a post-hoc observation that six of nine deaths associated with suboptimal care occurred early in the study period, it may be noteworthy that in the year 2007 and 2008 some new therapeutic and diagnostic measures were introduced in Norway (i.e. therapeutic hypothermia and ST-analysis (STAN)). It may also be noteworthy that there has been a decrease in the occurrence of cerebral palsy between 1999 and 2010, probably due to overall improvement in antenatal, obstetric and neonatal care [
25].
Implication
Since all case deliveries were in line with current Norwegian guidelines the question may arise if these guidelines may be improved, or even completely replaced by a general recommendation to deliver all fetuses in breech by planned CD. Regarding the latter option, we have previously reported that the absolute risk for death associated with vaginal breech delivery is very low, and does not differ from the risk associated with planned CD, although it was slightly higher than for vaginal delivery in cephalic presentation [
8]. The results of the present audit identifying several misclassified cases in the register suggest that the already very low absolute risk for death associated with vaginal breech delivery reported in the previous register-based study is probably even lower. Nonetheless, in line with the notion that “each baby counts” [
26], the potential avoidable death of 12 newborns in our study is worrying. On the other hand, we found evidence of continuing improvement in the clinical management of vaginal breech deliveries, as the majority of deaths associated with suboptimal care occurred before 2003. There are also concerns regarding the future health of children born by CD, and regarding maternal and infant complications in subsequent pregnancies [
1]. Based upon the results of our previous study, we estimate that to save one child, 500–600 mothers with a healthy baby presented in breech would need to have a CD [
8]. As a comprehensive interpretation of the results of our previous population-based study, and the present audit, we therefore do not find it justified to recommend that current guidelines regarding vaginal breech delivery are replaced.
A secondary advantage of not replacing these guidelines is that obstetricians retain their skills in vaginal breech delivery which may benefit management of the deliveries of the 20–30% of fetuses in undiagnosed breech presentation and also of twin births with the first or second twin in breech presentation [
27].
Regarding potential improvements of the guidelines, current Norwegian guidelines suggest that fetuses with an estimated weight between 4.0 and 4.5 kg may be suitable for vaginal delivery. This criterion is higher than the upper weight limit of 3.8–4.0 kg recommended in most other national guidelines [
14,
28,
29]. In our study a stricter weight criterion for vaginal delivery might have prevented one death. However a recent study published in 2018 did not report increased infant morbidity after delivery of infants with a birthweight between 3.8 and 4.5 kg compared to those with a birthweight below 3.8 kg [
30]. Another potential improvement of the guidelines might be to recommend pelvimetry in all cases of breech presentation before the decision of mode of delivery, since difficult delivery of the head was observed in four case deliveries. In the current Norwegian guidelines, pelvimetry may be done at the discretion of the responsible obstetrician. However, in two of these four difficult deliveries, pelvimetry had been done, in a further case, the mother was multipara (i.e. indicating appropriate pelvic size), and in the fourth case, pelvimetry could not be performed since breech presentation was diagnosed late in labour. Moreover, the evidence regarding whether pelvimetry may improve outcome of vaginal breech delivery is weak [
31]. Thus, the present study did not identify issues that could lead to recommending changes in the current Norwegian guidelines. Vaginal delivery in upright position [
32] was not observed in any of the deliveries included in this study. It is however, likely that delivery in upright position will be introduced as a recommended option for breech vaginal delivery in the next version of the Norwegian guidelines.
In 30% of all deliveries, breech presentation was not diagnosed before birth and one might speculate if ultrasound examination of the fetus late in pregnancy should be performed to confirm cephalic or breech presentation. Antenatal knowledge of fetal presentation might allow better planning of mode of delivery. In a recent study [
33] including assessment of the cost effectiveness of universal ultrasound scanning near term of nulliparous women, the authors concluded that this examination would virtually eliminate undiagnosed intrapartum breech presentation. If the examination could be conducted by midwives using a portable ultrasound system, this would most likely be cost effective [
33]. This would also make it possible to offer external cephalic version to more women eligible for this procedure [
34‐
36]. However, consistent with earlier studies, the proportion of infants in undiagnosed breech presentation did not differ between case and control deliveries. Thus, it is unclear if the introduction of late US examination will improve survival taking into consideration the currently observed quality of breech deliveries in Norway.
In the assessment of optimal care, we considered six of the 12 potential avoidable deaths to be associated with suboptimal intrapartum care. In all of these cases, CTG was misinterpreted. Such misinterpretation occurs regardless of fetal presentation, and underscores the need for rigorous training of obstetricians in the assessment of pathological CTG. The authors of this study deem it necessary to interpret CTG in a consistent manner, regardless of fetal presentation.
In the discussion with the mother regarding the choice of mode of breech delivery it should be emphasized that unexpected acute complications may occur in vaginal breech delivery as well as in vaginal cephalic delivery, despite adherence to guidelines. However, even though some of these complications are more likely to occur in breech than in cephalic presentation they are extremely rare.
Finally, the review of the hospital records revealed that five of 31 case deliveries recorded in the MBRN as singletons without congenital anomalies in breech presentation were misclassified. An additional implication of the present study is therefore that, in line with a study by Goffinet et al. [
37], results of large register-based studies need to be validated by in-depth studies.
Future research may address perinatal mortality and morbidity related to vaginal breech deliveries dependent on different guidelines and clinical handling in for example the Nordic countries or between other high-income countries.