Neonatal mortality in infants born weighing 501 to 1000 grams. The influence of changes in birth weight distribution and birth weight-specific mortality rates on neonatal survival.

We analyzed changes over time in neonatal mortality rates for infants born weighing 501 to 1000 gm. The decline in total mortality in this weight group due to improved small-group, birth weight-specific mortality was contrasted to the increase in mortality caused by changes in the birth weight distribution resulting from the care of smaller infants. Had the birth weight distribution remained unchanged, the total improvement in neonatal mortality for the entire 501 to 1000 gm group would have been substantially greater.