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Assessing the optimal time interval between growth measurements using a combined data set of weights and heights from
Charlotte Margaret Wright1, Caroline Haig2, Ulla Harjunmaa3
1Department of Child Health, School of Medicine, Nursing and Dentistry, University of Glasgow, Glasgow, UK charlotte.wright@glasgow.ac.uk.
Insights
Infant growth monitoring requires careful consideration of measurement intervals. Shorter intervals (2 weeks) increase the risk of misinterpreting growth faltering due to measurement noise, especially after 6 months of age.
Area of Science:
- Pediatrics
- Growth Monitoring
- Biostatistics
Background:
- Current infant growth measurement interval guidelines lack evidence.
- Routine data can explore measurement error and short-term variation impacts on infant growth signals.
Purpose of the Study:
- To investigate the influence of measurement error and short-term variation on infant weight and length gain interpretation across different measurement intervals.
- To provide evidence-based recommendations for optimal infant measurement frequency.
Main Methods:
- Utilized a large dataset of infant weights and lengths (0-12 months) from 5948 infants.
- Extracted measurement pairs at 2, 4, and 8-week intervals.
- Modeled the impact of estimated measurement noise (116 g for weight, 0.5 cm for length) on growth velocity centiles and the likelihood of observing no growth.
Main Results:
- Average infant weight and length gain exceeded measurement variation over 4- and 8-week intervals.
- Measurement noise reduced the extremity of apparent growth velocities, particularly after 6 months.
- A 16% risk of no apparent growth was observed with 2-week intervals by 10 months of age.
Conclusions:
- Infant growth velocity over 4-8 week intervals is unlikely to be obscured by measurement noise.
- Measurements taken at 2-week intervals or less require caution when assessing growth faltering in infants over 6 months old.
- Evidence-based guidelines are needed for optimal infant measurement frequency to accurately track growth.
Background:
Current guidance on the optimum interval between measurements in infancy is not evidence based. We used routine data to explore how measurement error and short-term variation ('noise') might affect interpretation of infant weight and length gain ('signal') over different time intervals.
Method:
Using a database of weights and lengths from 5948 infants aged 0-12 months, all pairs of measurements per child 2, 4 and 8 weeks apart were extracted. Separately, 20 babies aged 2-10 months were weighed on six occasions over 3 days to estimate the SD of the weight difference between adjacent measurements (=116 g). Values of 116 g and 0.5 cm for 'noise' were then used to model its impact on (a) the estimated velocity centile and (b) the chance of seeing no growth during the interval, in individuals.
Results:
The average gain in weight and length was much larger than the corresponding SD over 8-week and 4-week time intervals, but not over 2 weeks. Noise tended to make apparent velocity less extreme; after age 6 months, a 2-week velocity that appeared to be on to the ninth centile, would truly be on the second-third centile if measured with no noise. For 2-week intervals, there was a 16% risk of no apparent growth by age 10 months.
Conclusions:
Growth in infancy is so rapid that the change in measurements 4-8 weeks apart is unlikely ever to be obscured by noise, but after age 6 months, measurements 2 weeks or less apart should be treated with caution when assessing growth faltering.
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