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Small for Gestational Age Coded Diagnoses in Aotearoa New Zealand's Administrative Health Datasets: A Validation
Mei-Ling Blank1, Sarah Donald1,2, Lianne Parkin1,2
1Department of Preventive and Social Medicine (Te Tari Hauora Tūmatanui) University of Otago (Ōtākou Whakaihu Waka) Dunedin New Zealand.
Insights
Routinely collected health data inaccurately codes small for gestational age (SGA) infants. Researchers should use birthweight calculators instead of ICD-10-AM codes for accurate SGA research in New Zealand.
Area of Science:
- Medical Informatics
- Neonatal Research
- Public Health Data Analysis
Background:
- Accurate identification of small for gestational age (SGA) infants is crucial for research utilizing routinely collected health data.
- Inconsistent coding practices for SGA infants can significantly impact the validity and reliability of research findings.
- This study addresses the implications of inaccurate SGA coding in New Zealand's health data.
Purpose of the Study:
- To estimate the sensitivity and specificity of coded SGA diagnoses in New Zealand's hospitalisation and mortality data.
- To determine if coding accuracy for SGA varies based on infant, pregnancy, and maternal characteristics.
- To provide recommendations for improving SGA data accuracy in population-level research.
Main Methods:
- Utilized New Zealand national health data (2005-2020) for 887,871 infants.
- Estimated birthweight centiles using Fenton and GROW calculators.
- Compared calculator-derived SGA status with ICD-10-AM coded SGA diagnoses (P051).
- Employed generalized linear models to calculate sensitivity and specificity ratios, adjusting for covariates.
Main Results:
- Coded SGA diagnoses showed low sensitivity (13.1% vs. Fenton, 9.8% vs. GROW) but high specificity (99.3% vs. Fenton, 99.7% vs. GROW).
- Significant discrepancies exist between coded SGA diagnoses and calculator-derived classifications.
- The proportion of SGA infants identified by calculators (9.1%-15.6%) far exceeded those with coded diagnoses (1.8%).
Conclusions:
- Relying on ICD-10-AM coded SGA diagnoses in New Zealand health data is unreliable for research.
- Population-level research on SGA should utilize validated birthweight calculators for accurate infant classification.
- Improved data ascertainment methods are needed to ensure the integrity of SGA research.
Background And Aims:
Inaccurate coding of small for gestational age (SGA) infants in routinely collected health data has implications for research based on those data. We aimed to estimate the sensitivity and specificity of coded SGA diagnoses in New Zealand's routinely collected hospitalisation and mortality data, and determine whether sensitivity and specificity varied by infant, pregnancy, and maternal characteristics.
Methods:
We estimated birthweight centiles of live and stillborn infants delivered in New Zealand between 2005 and 2020 using the Fenton Population Reference Calculator and the GROW Customised Bulk Centile Calculator (New Zealand version); values of the relevant variables (including gestational age, birthweight, infant sex, and others) were sourced from routinely collected national health data. We compared the SGA status derived from the calculators with coded SGA diagnoses (ICD-10-AM P051) in hospitalisation and mortality data. We estimated sensitivity and specificity ratios comparing coded diagnoses with each of the birthweight calculators using a generalised linear model, adjusting for infant, pregnancy, and maternal characteristics.
Results:
This analysis included 887,871 infants, with 15,850 (1.8%) having a coded SGA diagnosis. By contrast, the number and proportion of babies classified as SGA using the Fenton and GROW calculators were 80,541 (9.1%) and 138,866 (15.6%), respectively. Overall, compared with the Fenton calculator, the sensitivity of coded SGA diagnoses was 13.1% (specificity 99.3%). Compared with the GROW calculator, the sensitivity was 9.8% (specificity 99.7%).
Conclusion:
In New Zealand, population-level research involving SGA diagnoses should derive birthweight centiles using an appropriate calculator instead of using ICD-10-AM coded diagnoses.
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