Global Reference for Birthweight Predicts Mortality in Preterm Infants

Use of the newer Global Reference for fetal-weight and birthweight percentiles increases the identification of infant deaths by improved classification of abnormal newborn size at birth, concluded the authors of a new population-based cohort study.¹
   
Before the development of the Global Reference for fetal weight and birthweight percentiles (Global Reference), the available birthweight references were not applicable to all populations because they did not account for regional and population differences. Because of these differences throughout the world, a universal definition of small-for-gestational-age (SGA) has been challenging. In 2011, the Global Reference was introduced. This new generic reference was based on a fetal-weight reference and the concept of proportionality to allow for the weight reference to be adjusted according to the mean birthweight at 40 weeks’ gestation for any local population.²
   
To evaluate whether the Global Reference improves the definitions of SGA, appropriate-for-gestational-age (AGA), and large-for-gestational-age (LGA) in predicting infant mortality, the researchers compared infant mortality rates of SGA, AGA, and LGA as classified by 3 different references for fetal weight and birthweight-the Global Reference, a commonly used birthweight reference, and Hadlock’s ultrasound reference.
   
Of nearly 34 million eligible singleton liveborn infants, 25% of preterm infants and 9% of term infants were classified differently for SGA, AGA, and LGA by the Global Reference and a common birthweight reference. Higher mortality rates were noted for preterm SGA and preterm LGA infants when the Global Reference was used in comparison with the common birthweight reference. Infants classified as SGA by the Global Reference but not the common birthweight reference had a considerably higher mortality rate than those classified as SGA by the common birthweight reference but not the Global Reference (105.7 per 1000 vs 12.9 per 1000, respectively; relative risk, 8.17).
   
Among term infants, however, these differences in mortality diminished greatly. Yet compared with other races, AGA and LGA black infants had a higher mortality rate regardless of whether they were preterm or term.
   
According to the study authors, use of the Global Reference, compared with a common birthweight reference, can better predict infant mortality by improved classification of abnormal newborn size at birth, especially in preterm infants.¹

Pertinent Points:
- Improved classification of small-for-gestational-age (SGA) infants, especially SGA preterm infants, can better predict infant mortality.
- The mortality rates of infants classified as SGA by the Global Reference was considerably higher than those classified as SGA by a common birthweight reference.
 

References:

1. Ding G, Tian Y, Zhang Y, et al. Application of a global reference for fetal-weight and birthweight percentiles in predicting infant mortality. BJOG. 2013 Jul 17. doi: 10.1111/1471-0528.12381. [Epub ahead of print]
2. Mikolajczyk RT, Zhang J, Betran AP, et al. A global reference for fetal-weight and birthweight percentiles. Lancet. 2011;377:1855-1861.