[Underreporting of first-week mortality in premature childbirth in the National Obstetrics Register].

The reliability of the perinatal mortality as recorded in the Perinatal Database of the Netherlands (LVR), was studied over 1983. For this year is was possible to make a comparison between preterm infants in the LVR and the same infants recorded by paediatricians in the database of the Project on Preterm and Small for Gestational Age Infants in the Netherlands 1983 (POPS). The comparison between the recorded mortality of the same infants in these two anonymous databases was realised by a simple matching procedure. For the premature infants a 30% lower first week mortality was found in the LVR than in the POPS-group, which means that 10% of the total perinatal mortality (stillbirths and first-week deaths together) has not been registered in the LVR for this group, due to lack of adaptation of data after later deaths. The mortality in the LVR should be interpreted with caution while it is not yet possible to match the obstetric data to the data of the National Neonatology Registration.