Abstract
Background. Dystocia--prolonged and difficult labor--is a common and worldwide problem during parturition. Epidemiological studies have suggested a familial aggregation. This study aimed to quantify the genetic influence (i.e. the heritability) on dystocia. Methods. A retrospective study of all births in Sweden from 1973 through 1997 was undertaken. Data from the population-based Swedish Birth, Twin and National Family Registers were linked on an individual basis. In total, 2 539 534 births were analyzed. Relationships between sibling and mother-daughter pairs were established. The relative risk for dystocia was calculated. Model-fitting (Mx) was used to estimate the relative contribution of genetic and environmental factors for liability to dystocia. Results. In all, 190 747 women were diagnosed with dystocia. Measures of familial similarity (relative risks and correlation of liability) for dystocia were higher in monozygotic than in dizygotic twins, other sibling pairs and mother-daughter pairs. Correlation of liability was also higher in full-sisters than in half-sisters. Model-fitting suggested that genetic effects accounted for 28%[95% confidence interval (CI) 21-32] of the susceptibility for dystocia. Conclusion. Dystocia is a complex disorder of poor uterine action that is influenced by a significant genetic component as well as environmental factors. The amount of genetic influence makes it interesting to study the gene expression in these patients. Detection of the genes related to dystocia might lead to better pathophysiological understanding of this condition and the possibility of detecting these mothers before parturition.