Twenty-two studies involving 7,239 breech deliveries, with an average of 329 breech deliveries per study (range: 109 to 899). The majority of the studies were retrospective; only 2 prospective and randomised studies, and 3 prospective and non-randomised studies, were included.
The average proportion of vaginal deliveries performed was 48% (range: 24 to 81). Vaginal delivery was attempted in 62% of the patients (range: 33 to 86), and was finally achieved in 46% (range: 29 to 81). The great variability of the rate of vaginal delivery attempted, or finally achieved, was linked to the heterogeneity of the methodology and criteria used in all of those studies.
Perinatal mortality.
The meta-analyses of perinatal mortality did not reveal a significant increased risk. When comparing the vaginal route with that of Caesarean section (7,239 breech deliveries), the pooled OR was 1.90 (95% CI: 0.59, 8.22). When comparing the number of vaginal deliveries attempted with the number of planned Caesareans (4,120 breech deliveries), the pooled OR was 4.95 (95% CI: 0.44, 80.06).
Neonatal morbidity.
The neonatal morbidity showed an increased risk with vaginal delivery. When comparing vaginal and Caesarean delivery, the pooled OR was 2.42 (95% CI: 1.86, 3.42) for Apgar scores less than 7 at 1 minute (1,696 breech deliveries), and 2.25 (95% CI: 1.12, 4.49) for Apgar scores less than 7, at 5 minutes (2484 breech deliveries). When comparing the neonatal morbidity (as defined by each author) for vaginal delivery and Caesarean section (3,689 breech deliveries), the pooled OR was 3.67 (95% CI: 2.10, 5.82).
The Apgar scores at 1 and 5 minutes were defined identically in most studies. However, several studies differed in the definition of perinatal morbidity.