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Why infant very low birthweight rates have failed to decline in the United States vital statistics.

BACKGROUND
Very low birthweight (VLBW) rates, i.e. births of < 1500 g, have been long established as the major determinant of outcome for infants. Nevertheless, despite much medical, political and social effort, these rates have not declined during the past 40 years in the US Vital Statistics. To explore the causes of this disturbing finding, trends in low birthweight distribution at a community hospital and the Vital Statistics data were investigated.


METHODS
The weights of livebirths and foetal deaths (27,944 births) at a community hospital during three 5-year periods, 1973-1987, were examined for trends in low birthweight (LBW) distribution, and they were contrasted with the US Vital Statistics.


RESULTS
For white infants weighing 500-999 g the livebirth rates declined from 3.7 per 1000 births in period one to 1.1 per 1000 in period three (70.2%); for white infants 1000-1499 g, livebirths declined from 4.2 to 3.2 per 1000. Hospital white livebirths < 2500 g declined 18.7% from the first to the third period. Among black livebirths the LBW rate also declined from 126.4 per 1000 in period one to 85.4 per 1000 in the third period. Foetal deaths declined from 8.2 per 1000 births to 6.2 per 1000 in period three, a 24.4% decline. However, foetal deaths < 500 g increased 411%, from 3.6% of the total foetal deaths in period one to 18.4% in the third period.


CONCLUSION
Increasing registration of births in the US may have hidden a marked improvement in the VLBW problem. More complete registration of births and changes in the perception of viability appear responsible for the artefact.