Background: In populations with a high incidence of low birth weight, a macrosomia index (ratio of head /chest circumference) may better detect infants of diabetic mothers rather than a birth weight of ≥4000g. The objective of this study was to correlate Macrosomia Index ≤1 (MI) with maternal HbA1c at delivery.Methods: Prospective cross-sectional study in a Medical College Hospital in South India from November 2012 to March 2014.  Study subjects were 715 term consecutive, mother/neonate pairs, booked, inborn and singleton deliveries. Birth weight, head and chest circumference of neonates, and maternal HbA1c at delivery were measured. The calculated macrosmia index (MI) was correlated with maternal HbA1c. Pearson correlation and odd’s ratio were calculated.Results: Of 715 mothers, 68.3% (488/715) had HbA1c >5.4% (range 4.2 to 10.5%), although only 32.7% (234/715) were categorized as gestational diabetics in pregnancy. Odds of Macrosomia Index ≤1 in neonates with maternal HbA1c > 5.4% was 7 times (95%CI: 3.2-15.4) as compared to that of neonates of mothers with HbA1c ≤ 5.4 (p<0.001). 13.4% (96/715) of neonates had MI ≤1 but only 1.4% (10/715) had birth weight of ≥4000g.Conclusions: MI ≤1 correlated with an HbA1c of >5.4% at delivery. Hence, in addition to birth weight ≥4000g, MI ≤1 should also be used to detect macrosomia in infants of diabetic mothers.

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