Comparison of Size Determination Using Fenton and World Health Organization Growth Charts in Term Infants

To test the hypothesis that classification as small for gestational age (SGA), appropriate for gestational age (AGA), or large for gestational age (LGA) among term infants would systematically differ between Fenton and World Health Organization (WHO) and that these differences would impact clinical care regarding postnatal glucose screening.

All infants born over 3 years (1/1/2020-12/31/2022) between 37-0/7 and 41-6/7-weeks gestational age in one rural, one suburban, or one urban hospital affiliated with an academic medical system in central North Carolina were included.

Among 10,825 newborns, weight classifications by Fenton and WHO as SGA, AGA, and LGA were concordant for 71%. Among the 29% with discordant classifications, approximately one-third were SGA by Fenton and AGA by WHO, and two-thirds were LGA by WHO and AGA by Fenton. The discordance decreased from 42% at 37-weeks to 6% at 41-weeks gestational age (P < .001). The discordance was higher for male than female newborns (31% vs. 27%, P < .001). The Kappa coefficient increased by gestational age after 38 weeks and was higher for female than male newborns. While more newborns will be classified as either SGA or LGA using WHO than Fenton (32% vs. 25%, P < .001), the minimum duration of postnatal glucose screening using 2011 AAP guidelines is longer for SGA (24 hours) than LGA (12 hours) infants, resulting in a lower cumulative minimum duration with WHO.

The classification of birth weight by WHO and Fenton growth charts varies across gestational age and sex and has clinical implications regarding postnatal glucose screening.