BIRTH-WEIGHT AND PERINATAL-MORTALITY - A COMPARISON OF THE UNITED-STATES AND NORWAY

Objective.-To compare perinatal mortality in the United States and Nor way, using a new analytic approach based on relative birth weight. Des ign.-Comparison of linked birth and perinatal death records for US and Norwegian births from 1986 through 1987, the most recently available 2-year period. Setting.-Norway and the United States. Participants.-A total of 7 445 914 US births and 105 084 Norwegian births. Interventio ns.-None. Main Outcome Measure.-Perinatal weight-specific mortality af ter adjustment for each country's own mean birth weight. Results.-The higher rate of perinatal death in the United States compared with Norw ay is due to an excess of preterm deliveries in the United States. Low -weight, preterm births comprise 2.9% of US births compared with 2.1% of Norwegian births. If the United States could eliminate this slight excess of preterm delivery, perinatal mortality in the United States w ould decrease to the level in Norway. Unexpectedly, the survival of ne wborns at any given birth weight is virtually the same in the United S tates and Norway when newborns' birth weights are considered relative to their own nation's mean weight. Conclusions.-Low rates of perinatal mortality in the Scandinavian countries have usually been attributed to the heavier weights of their newborns. Higher mortality among US in fants is in fact due entirety to a small excess of preterm deliveries. The lighter weights of US newborns at term appear not to affect perin atal survival. Furthermore, the apparent survival advantage of low-wei ght US newborns (used by policymakers as evidence of superior US inten sive neonatal care) may be at [east partly an artifact. When weight-sp ecific mortality rates are adjusted to relative birth weight, low-weig ht newborns have the same survival in Norway as in the United States. The prevention of excess mortality among US infants depends on the pre vention of preterm births, not on changes in mean birth weight.