Do 3D fetal thigh measurements correlate with body composition in early childhood?

Previous studies have shown a correlation between total thigh volume (TTV) and percent body fat (PBF) in infants. In fetuses with an estimated fetal weight (EFW) < 10th centile, TTV has been found to discriminate between fetal growth restricted (FGR) and small for gestational age (SGA) fetuses by ISUOG’s Delphi consensus. Therefore, we have examined whether: Proportion of fat in the fetal thigh correlated with PBF in early childhood. There is a difference in percent childhood fat deposition (CFD) in those with FGR vs. SGA according to the Delphi consensus. There was a change in the ratio of fat mass volume (FMV) to lean mass volume (LMV) in fetuses over time with an EFW < 10th centile. 3D sweeps of the fetal thigh were performed in patients with EFWs < 10th centile after 25 weeks. Using a method by Lee et al., TTV and LMV were calculated. FMV was derived by subtracting LMV from TTV. Measures closest to delivery were used to compare FGR and SGAs. PBF was assessed in children aged 2-5 years using air displacement plethysmography. Differences in percent CFD were calculated by taking the absolute difference between percent fetal thigh fat (FMV/TTV) and PBF in childhood. Growth restricted TTVs and FMV/LMV ratios were plotted by gestational age. Spearman’s correlation was computed to assess the relationship between FMV/TTV and PBF in childhood. Percent CFD was compared in FGR vs. SGAs with an independent samples t-test. Mean TTVs were lower at all gestational ages in this growth restricted cohort compared to control values (Figure 1a). The FMV/LMV ratio remained flat throughout late gestation (Figure 1b). There was no significant relationship between FMV/TTV and PBF in children (Figure 1c, p=0.33). Percent CFD was similar between FGR and SGAs (FGR: 35.8% ± 10.0%, SGA: 30.3% ± 11.4%, p=0.20). Although all 3 fetal thigh measurements relate to the degree of overall in-utero deprivation in FGR, they may not predict the trajectory of catch-up growth in early childhood, which did not differ between FGR and SGA fetuses in this small sample.