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The pitfalls of using birthweight centile charts to audit care

journal contribution
posted on 12.11.2020, 00:25 by RJ Selvaratnam, Mary-Ann Davey, EM Wallace
© 2020 Selvaratnam et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Objectives: Timely delivery of fetal growth restriction (FGR) is important in reducing stillbirth. However, targeted earlier delivery of FGR preferentially removes smaller babies from later gestations, thereby right-shifting the distribution of birthweights at term. This artificially increases the birthweight cutoffs defining the lower centiles and redefines normally grown babies as small by population-based birthweight centiles. Our objective was to compare updated Australian national population-based birthweight centile charts over time with the prescriptive INTERGROWTH-21st standard. Methods: A retrospective descriptive study of all singleton births ≥34 weeks' gestation in Victoria, Australia in five two-year epochs: 1983-84, 1993-94, 2003-04, 2013-14, and 2016-17. The birthweight cutoffs defining the 3rd and 10th centile from three Australian national population-based birthweight centile charts, for births in 1991-1994, in 1998-2007, and 2004-2013 respectively, were applied to each epoch to calculate the proportion of babies with birthweight <3rd and <10th centile. The same analysis was done using the INTERGROWTH-21st birthweight standard. To assess change over gestation, proportions were also calculated at preterm, early term and late term gestations. Results: From 1983-84 to 2016-17, the proportion of babies with birthweight <3rd fell across all birthweight centile charts, from 3.1% to 1.7% using the oldest Australian chart, from 3.9% to 1.9% using the second oldest Australian chart, from 4.3% to 2.2% using the most recent Australian chart, and from 2.0% to 0.9% using the INTERGROWTH-21st standard. A similar effect was evident for the <10th centile. The effect was most obvious at term gestations. Updating the Australian population birthweight chart progressively right-shifted the birthweight distribution, changing the definition of small over time. The birthweight distribution of INTERGROWTH-21st was left-shifted compared to the Australian charts. Conclusions: Locally-derived population-based birthweight centiles are better for clinical audit of care but should not be updated. Prescriptive birthweight standards are less useful in defining 'small' due to their significant left-shift.

Funding

This work was undertaken as part of a National Health and Medical Research Council (NHMRC) funded Program Grant (APP1113902) to EMW. RJS received an Australian Government Research Training Program (RTP) Scholarship from Monash University and a top-up scholarship from the national Stillbirth Centre of Research Excellence (CRE). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.We are grateful to Consultative Council on Obstetric and Paediatric Mortality and Morbidity (CCOPMM) for providing access to the data used for this project and for the assistance of the staff at the Consultative Councils Unit, Safer Care Victoria. The views expressed in this paper do not necessarily reflect those of CCOPMM.

National Health and Medical Research Council (NHMRC) | APP1113902

Australian Government Research Training Program (RTP) Scholarship from Monash University

national Stillbirth Centre of Research Excellence (CRE)

History

Publication Date

23/06/2020

Journal

PLoS One

Volume

15

Issue

6

Article Number

ARTN e0235113

Pagination

10p.

Publisher

Public Library of Science

ISSN

1932-6203

Rights Statement

The Author reserves all moral rights over the deposited text and must be credited if any re-use occurs. Documents deposited in OPAL are the Open Access versions of outputs published elsewhere. Changes resulting from the publishing process may therefore not be reflected in this document. The final published version may be obtained via the publisher’s DOI. Please note that additional copyright and access restrictions may apply to the published version.

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