Objective: To analyze the exhaustiveness and reliability of the data on perinatal mortality in two Spanish registries, namely, the National Statistics Institute and the Perinatal Mortality Registry of the Valencian Community and to calculate and compare the perinatal mortality rate (PMR) and its components in native and immigrant women, based on the cases reported to both registries in 2005 and 2006.
Methods: Perinatal mortality and its components were defined according to the World Health Organization's criteria. The magnitude of underreporting was calculated by taking into account the frequencies and percentages of deaths not declared for 2005-2006. Rates and their 95% confidence intervals were calculated and compared between native and immigrant women using data from both registries.
Results: Fetal and neonatal deaths were substantially underreported in the National Statistics Institute compared with the Perinatal Mortality Registry of the Valencian Community. Moreover, in the National Statistics Institute, some neonatal deaths among the offspring of immigrant women were misclassified as being of Spanish nationality. These two factors distorted the proportion of fetal and neonatal deaths in immigrant women, giving rise to an underestimation of the PMR and its components, since the rates obtained from the Perinatal Mortality Registry of the Valencian Community were higher in immigrant than in Spanish women, particularly among east-European and sub-Saharan women.
Conclusions: Our results indicate that both registries are complementary. However, the Perinatal Mortality Registry of the Valencian Community was found to be more exhaustive and to have greater reliability. Our results also suggest the importance of monitoring trends in PMR in the immigrant population in Spain.