Errors in registered birth weight and its implications for mortality statistics

Background-Birth weight mortality statistics are important for examining tr ends and monitoring the outcomes of neonatal care. Aim-To determine the effects of errors in the registered birth weight on bi rth weight specific mortality. Methods-All twins born in England and Wales during 1993-95 comprise the den ominator population. For those twins that died, the Office for National Sta tistics (ONS) provided copies of the death certificates. From the informati on on the death certificates, the registered birth weight was validated and amended using predetermined rules. The neonatal, postneonatal, and infant mortality rates were recalculated. Results-In 2.5% of cases the registered birth weight was "not stated" and i n others there were miscoding errors. Important differences between publish ed and amended birth weight specific mortality rates especially in <500 g a nd <greater than or equal to>3500 g groups were evident. Conclusions-The bias arising from these errors should be taken into account in interpreting mortality rates and their trends.