Secular Trends in Birthweights in Two Epochs Over 40 Years in a Tertiary Care Center

To compare the average birthweights and the weight centiles of the 'new' growth charts with the 'old' (1974) charts developed in the same unit four decades ago.

Birthweight and gestation data of the eligible 12,355 singleton neonates born between 2009 and 2016 at a level-3 neonatal unit at a public sector hospital were used to develop the new growth chart. We then compared the prevalence of small for gestational age (SGA) and large for gestational age (LGA) classified by the new charts and the old charts, the incidence of short-term adverse outcomes among them, and the diagnostic performance of both the charts to identify the adverse outcomes in a separate validation cohort.

The mean birthweights of boys and girls across all gestations were higher by 150-200 g and 100-150 g, respectively, in the new chart. The prevalence of SGA doubled (9.8% vs 4.7%), but LGA decreased by one-third (17.5% vs 25.9%) with the new chart. However, the proportion of SGA and LGA having one or more short-term adverse outcomes, and the diagnostic performance of both the charts to identify neonates with short-term adverse outcomes, were comparable.

There was an upward shift in the birthweights by about 150 g across all gestations in the new chart compared to the old chart developed 40 years ago. The findings imply the need to consider using updated growth charts to ensure accurate classification of size at birth of neonates.