Assessing the role of maternal race on the prediction of NICU admission by three growth charts: a cross-sectional study

Abstract

Background The National Institutes of Health (NIH) race-specific and Intergrowth 21st race-independent fetal growth standards have recently been developed to assess fetal growth although the Alexander reference has been commonly used for over two decades. Societies are becoming increasingly stratified by race, and thus fetal growth effects are increasingly socially-derived. Relatedly, there is discussion surrounding the utility of classifying fetal growth on the basis of ideal growth versus typical growth. Therefore, we aimed to evaluate the classification discrepancies for small for gestational age (SGA) or large for gestational age (LGA) infants between growth charts, stratified by maternal race; and to determine which chart most accurately identifies vulnerable infants requiring NICU (Neonatal Intensive Care Unit) admission. Methods This cross-sectional study examined singleton liveborn infants born between 33 and 42 weeks of gestation with a self-identified White, Black, Hispanic, or Asian mother. Data were obtained from the 2014 National Centre of Health Statistics’ Vital Statistics Natality files. SGA infants were considered those <10th percentile and LGA were those >90th percentile, for each growth chart. SGA and LGA classification by maternal race was evaluated using stratified analysis and logistic regression. Odds ratios and goodness of fit characteristics were assessed to determine which chart best predicted NICU admission. Results In our sample of 3,782,660 singleton infants, significantly different proportions of infants were classified SGA/LGA using the Alexander (SGA: 4.6%, LGA:19.4%), Intergrowth 21st (SGA: 4.0%, LGA:19.6%), and NIH (SGA: 9.8%, LGA: 8.5%) charts. Race-specific classification of SGA differed by race and chart; there was an 8.4% difference in white infants considered SGA by Intergrowth (3.3; 95% CI, 3.2–3.3) compared to NIH (11.7%; 95% CI, 11.6–11.7). The NIH and Intergrowth 21st charts were typically in agreement for both SGA and LGA, differing substantially from the Alexander reference; however, there were significant differences between Intergrowth and NIH for proportions of SGA (NIH: 10.2%, CI 95%, 10.1–10.2; Intergrowth: 4.0%, CI 95%, 3.9–4.0) and LGA (NIH: 6.3%, CI 95%, 6.3–6.4; Intergrowth: 19.6%, CI 95%, 19.5–19.6) infants. Overall, 11.1% of Black infants were considered SGA by NIH and 6.8% by Intergrowth—more often than other races. Intergrowth classified the fewest infants as SGA and Alexander classified the most as SGA for all races. While NIH was better at discriminating LGA (OR: 2.72) and SGA-associated (OR: 1.71) NICU admissions compared to other charts, no standard was a significantly better predictor of NICU admission. Conclusion Since the NIH standard identified the fewest LGA infants and the Intergrowth 21st standard identified the fewest SGA infants, these charts may have been better identifiers of infants on either extreme of growth. The agreement between NIH and Intergrowth 21st charts suggest their interchangeable use for healthy populations, but the NIH may be more applicable given its racial stratification. However, the differences in proportions of SGA/LGA infants among the three charts according to maternal race introduce significant clinical ambiguity when identifying vulnerable infants. Additionally, no chart was able to accurately identify vulnerable infants and the dataset did not permit differentiation between growth-restricted and constitutionally small infants. Further work is necessary before selecting a true gold standard for use in routine clinical practice.