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Related Experiment Video

Updated: Aug 6, 2025

Fetal Echocardiography and Pulsed-wave Doppler Ultrasound in a Rabbit Model of Intrauterine Growth Restriction
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A new method for customized fetal growth reference percentiles.

Katherine L Grantz1, Stefanie N Hinkle2, Dian He1,3

  • 1Division of Population Health Research, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America.

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|March 17, 2023
PubMed
Summary

Customized fetal growth charts often assume normal birthweight distribution, but this study found this assumption flawed. A new heteroscedastic model may better detect abnormal fetal growth.

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Area of Science:

  • Obstetrics and Gynecology
  • Perinatal Medicine
  • Biostatistics

Background:

  • Customized fetal growth charts rely on assumptions of normally distributed birthweights and constant coefficient of variation.
  • The proportionality of standard deviation to the mean, a key aspect of these charts, has not been formally validated.

Purpose of the Study:

  • To investigate the validity of normality and constant coefficient of variation assumptions in customized fetal growth charting.
  • To develop and evaluate a more flexible model for customizing fetal growth percentiles.

Main Methods:

  • Secondary analysis of NICHD Fetal Growth Studies-Singletons (n=2288) using longitudinal sonographic data.
  • Examined mean and standard deviation behavior using the Gardosi method.
  • Developed a heteroscedastic regression model and used quantile regression for percentile calculation.

Main Results:

  • Analysis of term birthweights challenged the normality and proportionality assumptions.
  • Standard deviation did not linearly correlate with mean birthweight, and normality-based percentiles deviated from empirical ones.
  • Neonatal morbidity/mortality rates were higher with heteroscedastic/quantile models compared to the Gardosi model, though prediction performance was similar.

Conclusions:

  • Findings question the normality and constant coefficient of variation assumptions inherent in the Gardosi customization method.
  • A heteroscedastic model can better account for unstable variance in customization, potentially improving the detection of abnormal fetal growth percentiles.