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An update of the Swedish reference standards for weight, length and head circumference at birth for given gestational
A Niklasson1, A Ericson, J G Fryer
1Department of Paediatrics I, University of Göteborg, Sweden.
Insights
This study updates Swedish birth weight, length, and head circumference standards using a large infant cohort. New reference charts account for birth weight distribution skewness, improving size deviation evaluation.
Area of Science:
- Pediatrics
- Neonatology
- Biostatistics
Background:
- Accurate reference standards are crucial for assessing infant growth and development.
- Existing Swedish reference standards required updating due to sample size and statistical considerations.
Purpose of the Study:
- To present updated Swedish reference standards for infant weight, length, and head circumference.
- To improve the evaluation of size deviation at birth by accounting for birth weight distribution characteristics.
Main Methods:
- Analysis of a large Swedish cohort of infants born between 1977-1981 (n=475,588).
- Extraction of a 'healthy population' using prospectively collected data.
- Application of square root transformation for skewed birth weight data and polynomial fitting for smoothing.
Main Results:
- Developed updated weekly reference values and charts for gestational ages 28-42 weeks.
- Established methods for calculating standard deviation scores for individual infants.
- Demonstrated improved accuracy by incorporating larger sample sizes and addressing birth weight skewness.
Conclusions:
- The updated reference standards provide a more accurate tool for evaluating infant size at birth.
- These standards facilitate better clinical assessment and comparison of infant growth trajectories.
- The methodology allows for continuous assessment and group comparisons.
Abstract:
An update of the Swedish reference standards for weight, length, and head circumference at birth, for each week of gestational age, is presented. It is based on the total Swedish cohorts of infants born 1977-1981 (n = 475,588). A "healthy population" (79%) was extracted, using prospectively collected data. Weekly (28-42 weeks) grouped data for length and head circumference were well approximated by the normal distribution, but the distributions for birthweight were positively skewed. The original skewed distributions for birthweight were transformed, using the square root, resulting in distributions close to the Gaussian. For smoothing purposes, the weakly values for the mean and the standard deviation were both fitted by a third degree polynomial function. These functions also make possible the calculation of the continuous variable, standard deviation score, for individual newborn infants as well as a comparison of distributions between groups of infants. The reference values and charts presented here have two major advantages over the current Swedish ones: the sample size used is now sufficiently large at the lower gestational ages, so that empirically found variations can be used, and the skewness of the birth weight distribution has been taken into account. The use of the reference standards presented here improves and facilitates evaluation of size deviation at birth.