To compare perinatal mortality in breech presentation delivered vaginally and by cesarean in individual births and in sibships.Methods
A national, population registry-based study, 1967–1994, was conducted, with maternal record linkage of sibships, comprising the first to the third birth of a mother. The main outcome was perinatal mortality. Odds ratios of perinatal mortality were calculated and adjusted by logistic regression analysis.Results
The overall relative perinatal mortality was 4.3 (95% confidence interval [CI] 4.1, 4.5) in breech compared with nonbreech presentation and 5.4 (95% CI 4.7, 6.2) in vaginal compared with cesarean delivery. The relative perinatal mortality in breech compared with nonbreech presentation was lowest in birth order one compared with birth orders two and three. In breech vaginal delivery compared with cesarean delivery, the opposite effect of birth order was found. The highest perinatal mortality was found in a current breech presentation of a sibship with no previous breech births. In birth subsequent to breech births, perinatal mortality was more or less independent of current presentation, without respect to delivery method. The increased perinatal mortality in breech presentation is explained partly by its association with other risk factors for perinatal death.Conclusion
Women with recurring breech presentation represent a lower risk of adverse perinatal outcome. This might be explained by a biologic mechanism or by increased quality of antenatal care. An increased mortality in subsequent nonbreech siblings after a breech presentation was surprising.