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Two definitions of "small size at birth" as predictors of motor development at six months
Olga Basso1, Morten Frydenberg, Sjurdur F Olsen
1Danish Epidemiology Science Centre, Department of Epidemiology and Social Medicine, University of Arhus, Arhus, Denmark. bassoo2@niehs.nih.gov
Insights
A new birth-weight ratio, comparing a baby to their sibling, better predicts developmental delays than the standard small-for-gestational-age (SGA) measure. This ratio identifies babies truly smaller than their family norm, not just those with small mothers.
Area of Science:
- Perinatal medicine
- Pediatric development
- Biostatistics
Background:
- Infants born small are at higher risk for adverse outcomes.
- Standard small-for-gestational-age (SGA) z-score may not fully capture individual risk.
- Family norms, using sibling birth weight, may offer a more personalized risk assessment.
Purpose of the Study:
- To compare the predictive accuracy of a novel birth-weight ratio with the standard SGA z-score for identifying at-risk infants.
- To evaluate how these two measures predict motor development.
- To assess the influence of birth weight predictors on infant classification.
Main Methods:
- Calculated birth-weight ratio (actual/sibling-predicted birth weight x 100) for 10,577 infants.
- Identified infants in the lowest decile of birth-weight ratio and SGA z-score.
- Compared motor development outcomes and predictor influences between the two classification methods.
Main Results:
- Birth-weight ratio and SGA identified similar numbers of infants (1058 vs 1059).
- A low birth-weight ratio showed a slightly better prediction of delayed motor development compared to SGA.
- Infants identified solely by SGA were more likely to have mothers who were small or smoked.
Conclusions:
- Combined use of birth-weight ratio and SGA enhances identification of at-risk infants.
- Birth-weight ratio is less influenced by maternal size, highlighting infants significantly smaller than their siblings.
- This ratio offers a more sensitive tool for identifying infants with substantial size deficits relative to family norms.
Background:
Small babies are known to be at increased risk for a wide range of difficulties. In predicting risk, it may be more informative to estimate smallness in relation to family norm (using the birth weight of an older sibling) rather than to use the standard "small-for-gestational-age" (SGA z-score) measure.
Methods:
For 10,577 babies born to women enrolled in the Danish National Birth Cohort, we calculated a "birth-weight ratio" (actual birth weight/expected birth weight predicted from older sibling x 100). We identified babies in the lowest decile of the birth-weight ratio (
Results:
Birth-weight ratio and SGA identified 1058 and 1059 babies, respectively, with 738 identified by both methods. A low birth-weight ratio predicted delayed motor development slightly better than did SGA. Babies classified as too small solely by the SGA criterion were more often born to small or smoking mothers than those identified solely by the birth-weight ratio.
Conclusions:
The combined use of the birth-weight ratio and SGA may provide a more sensitive tool for identifying babies at risk. The birth-weight ratio is less likely to classify babies as small based on their mothers' body size, identifying instead babies who were substantially smaller than their sibling.
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