Fractional fetal thigh volume in the prediction of normal and abnormal fetal growth during the third trimester of pregnancy

Abstract

BackgroundCurrently, 2-dimensional ultrasound estimation of fetal size rather than fetal growth is used to define fetal growth restriction, but single estimates in late pregnancy lack sensitivity and may identify small for gestational age rather than growth restriction. Single or longitudinal measures of 3-dimensional fractional thigh volume may address this problem.ObjectiveWe sought to derive normal values for 3-dimensional fractional thigh volume in the third trimester, determine if fractional thigh volume is superior to 2-dimensional ultrasound biometry alone for detecting fetal growth restriction, and determine whether individualized growth assessment parameters have the potential to identify fetal growth restriction remote from term delivery.Study DesignThis was a longitudinal prospective cohort study of 115 unselected pregnancies in a tertiary referral unit (St Mary’s Hospital, Manchester, United Kingdom). Standard 2-dimensional ultrasound biometry measurements were obtained, along with fractional thigh volume measurements (based on 50% of the femoral diaphysis length). Measurements were used to calculate estimated fetal weight (Hadlock). Individualized growth assessment parameters and percentage deviations in longitudinally measured biometrics were determined using a Web-based system (iGAP; http://iGAP.research.bcm.edu). Small for gestational age was defined <10th and fetal growth restriction <3rd customized birthweight centile. Logistic regression was used to compare estimated fetal weight (Hadlock), estimated fetal weight (biparietal diameter–abdominal circumference–fractional thigh volume), fractional thigh volume, and abdominal circumference for the prediction of small for gestational age or fetal growth restriction at birth. Screening performance was assessed using area under the receiver operating characteristic curve.ResultsThere was a better correlation between fractional thigh volume and estimated fetal weight ((biparietal diameter–abdominal circumference–fractional thigh volume) obtained at 34-36 weeks with birthweight than between 2-dimensional biometry measures such as abdominal circumference and estimated fetal weight (Hadlock). There was also a modest improvement in the detection of both small for gestational age and fetal growth restriction using fractional thigh volume–derived measures compared to standard 2-dimensional measurements (area under receiver operating characteristic curve, 0.86; 95% confidence interval, 0.79–0.94, and area under receiver operating characteristic curve, 0.92; 95% confidence interval, 0.85–0.99, respectively).ConclusionFractional thigh volume measurements offer some improvement over 2-dimensional biometry for the detection of late-onset fetal growth restriction at 34-36 weeks.

Individualized growth assessment: conceptual framework and practical implementation for the evaluation of fetal growth and neonatal growth outcome

“…Deviations from the predicted trajectory reflect differences between predicted and measured average growth rates for intervals starting at the beginning of the third trimester to any subsequent time point. These IGA concepts have been verified in four previous studies 89, 91–93 .…”

“…The user can interactively select which 2 nd trimester measurements are used to specify size models. Recently, the implementation of IGA for detection of late-onset fetal growth restriction (using iGAP software) was independently validated by Simcox et al in a longitudinal prospective cohort study of 115 pregnancies 93 . An evaluation of fetal growth restriction using iGAP is demonstrated in Figure 17.…”

ISUOG Practice Guidelines: ultrasound assessment of fetal biometry and growth

“…The concept of fractional limb volume was developed to improve the reproducibility and efficiency of manual tracing of fetal limb volumes. These measurements can serve as an index of fetal nutritional status and there are studies suggesting that combining fractional limb volume with 2D biometry improves the precision of EFW, with some improvement in detection of late‐onset FGR at 34–36 weeks.…”

A new customized fetal growth standard for African American women: the PRB/NICHD Detroit study

“…Although several studies suggest that estimates for the association between adverse neonatal outcomes and abnormal birthweight are higher for customized than non-customized (population-based) standards 31-37 , recent initiatives undertaken to develop growth standards proposed either population-based or only partially customized standards. For example, the INTERGROWTH-21 st study 16, 38-40 proposed a one-size-fits-all standard derived from a multi-ethnic population.…”