The Danish newborn standard and the International Fetal and Newborn Growth Consortium for the 21st Century newborn standard: A nationwide register-based cohort study

BACKGROUND: It is a matter of debate whether one universal standard such as Intergrowth-21st (IG-21) can be applied to all populations.

OBJECTIVE: We therefore aimed to establish a Danish Newborn Standard by the principles of the IG-21 Standard in order to compare the centiles of these two standards. A secondary objective was to compare the prevalence and the risk of fetal and neonatal death related to small-for-gestational-age (SGA) defined by the two standards when used in the Danish Reference Population.

STUDY DESIGN: Register-based nation-wide cohort study.The Danish Reference Population included 375,318 singletons born at 33-42 week's gestation in Denmark between January 1 2008 and December 31 2015. The Danish Standard Cohort included those 37,811 newborns who fulfilled the IG-21 Standard criterion. Birthweight centiles were estimated using smoothed quantiles for each gestational week. Outcomes were birthweight centiles, small for gestational age (SGA) defined by the 3rd centile, and adverse outcomes defined by either fetal or neonatal death.

RESULTS: At all gestational ages, the Danish Standard medians were higher than the IG-21 medians; at term by 295g for females and 320g for males. This resulted in different estimates of SGA prevalence within the entire population; 3.9% (n=14,698) using Danish Standard vs. 0.7% (n=2,640) using IG-21 Standard. Accordingly, the relative risk of fetal and neonatal death among SGA fetuses differed between SGA defined by different standards; RR=4.4 (Danish Standard) vs. RR=9.6 (Intergrowth-21st).

CONCLUSION: This finding does not support the hypothesis that one universal standard BW curve fits all populations.