Thresholds for small for gestational age among newborns of East Asian and South Asian ancestry

Objective — To determine the risk that newborn infants of East Asian and South Asian ancestry may be misclassified as small for gestational age (SGA).

Methods — We performed a single-centre, cross-sectional study of a cohort of liveborn infants born to women who had been born in Canada (n = 2362), East Asia (n = 1565) and South Asia (n = 753) and generated smoothed birth weight curves for males and females. We determined the rate of misclassification of infants of East Asian and South Asian maternal origin as SGA, using conventional weight centile cut-offs, rather than those specific to each ethnic group.

Results — Infants of Canadian-born mothers had a mean birth weight that was 144 g and 218 g greater than newborns of mothers of East Asian and South Asian origin, respectively. Using the 3rd centile cut-off for infants of Canadian-born mothers, 7 per 1000 female and 14 per 1000 male infants of East Asian maternal origin were potentially miscategorized as SGA at birth. Among female and male infants of mothers of South Asian origin, the corresponding rates were 29 and 46 per 1000.

Conclusion — Birth weight curves may need to be modified for newborns of East Asian and South Asian parentage to make a more accurate diagnosis of SGA.