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Fetal Size Classified Using Gestational Days rather than Gestational Weeks Improves Correlation with Stillbirth Risk: A Statewide Population Study.
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  • Natasha Pritchard,
  • Susan Walker,
  • Stephen Tong,
  • Anthea C. Lindquist
Natasha Pritchard
Mercy Hospital for Women

Corresponding Author:[email protected]

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Susan Walker
University of Melbourne
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Stephen Tong
University of Melbourne
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Anthea C. Lindquist
Mercy Hospital for Women
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Objective: Many growth charts provide single centile cutoffs for each week of gestation, yet fetuses gain weight throughout the week. We aimed to assess whether using a single centile per week distorts the proportion of infants classified as small and their risk of stillbirth across the week. Design: Retrospective cohort study. Setting: Victoria, Australia. Population: Singleton, non-anomalous infants born from 2005-2015 (529,261). Methods: We applied growth charts to identify small-for-gestational-age (SGA) fetuses on week-based charts (single centile per gestational week) and day-based charts (centile per gestational day). Main outcome measures: Proportions <10th centile by each chart, and stillbirth risk amongst SGA infants. Results: Using week-based charts, 12.1% of infants born on the first day of a gestational week were SGA, but only 7.8% on the final day; ie. an infant born at the end of the week was 44% less likely to be classed as SGA (p<0.0001). The relative risk of stillbirth amongst SGA infants born on the final day of the week compared with the first was 1.47 (95%CI 1.09-2.00, p=0.01). Using day charts, SGA proportions were similar and stillbirth risk equal between the beginning and end of the week (9.5% vs 9.9%). Conclusions: Growth standards using a single cutoff for a gestational week overestimate the proportion of infants that are small at the beginning of the week and underestimate the proportion at the end. This distorts the risk of stillbirth amongst SGA infants based on when in the week an infant is born. Day-based charts should be used
10 Jan 2022Submitted to BJOG: An International Journal of Obstetrics and Gynaecology
14 Jan 2022Assigned to Editor
14 Jan 2022Submission Checks Completed
15 Jan 2022Reviewer(s) Assigned
17 Feb 2022Review(s) Completed, Editorial Evaluation Pending
10 Aug 2022Published in PLOS ONE volume 17 issue 8 on pages e0271538. 10.1371/journal.pone.0271538