The Value Of Fractional Limb Volume Derived By Three-dimensional Ultrasound Combined With Two-dimensional Ultrasound Parameters In Estimating Fetal Weight And Predicting Macrosomia And Low-birth-weight Infants

ObjectiveFractional limb volume(FLV)is a newly developed three-dimensional ultrasound parameter of middle 50%limb volume of fetal upper arm and thigh(fractional arm volume,AVol,fractional thigh volume,TVol),which includes skin,subcutaneous tissue,fat,muscles and bones of 50%of the fetal middle limb.In this study,two-dimensional ultrasound was used to measure fetal routine ultrasound parameters,and three-dimensional ultrasound was used to measure AVol and TVol.The value of the above ultrasound parameters in evaluating fetal subcutaneous fat and estimating fetal body weight was discussed,and their application value in prenatal prediction of macrosomal infants and low-birth-weight infants was also discussed preliminarily.MethodsFrom October 2017 to April 2018,121 pregnant women who were examined and delivered at the affiliated provincial hospital of Anhui Medical University were selected.Fetal biparietal diameter(BPD),head circumference(HC),femur length(FL),abdominal circumference(AC)and thickness of soft tissue in middle thigh(FTSTT)were measured by two-dimensional ultrasound.Fetal AVol,TVol were obtained by three-dimensional ultrasound.The newborn’s skinfold thicknesses were measured in four positions:triceps brachii,biceps brachii muscle,superior iliac bone,and subscapular skin fold thickness in 24 hours postpartum,and the sum of skin fold thickness(SSFT)of the four positions was calculated.The correlation between ultrasonic parameters and fetal weight and SSFT was analyzed.A multivariate linear regression analysis was carried out with birth weight as dependent variable and ultrasonic parameter as independent variable to establish a model for predicting fetal weight.The receiver operating characteristic(ROC)curves of AVol,TVol for diagnosing macrosomia and low-birth-weight infants were plotted and their truncation values and their sensitivity and specificity were calculated.The consistency of AVol,TVol measurements within and between observers was analyzed.ResultsBPD,HC,FL,AC and FTSTT measured by two-dimensional ultrasound was(94.32±3.25)mm,(333.00±13.43)mm,(71.09±2.98)mm,(341.13±17.16)mm,(16.54±2.98mm;),respectively.The mean value of AVol,TVol measured by 3D ultrasound was(37.93±6.32)cm3,(88.63±20.57)cm3,respectively.There was no considerable intraobserver and interobserver variability in all ultrasound measurements of the same data(all P>0.05).Among 121 pregnant women,73 cases were transvaginal delivery and 48 cases were delivered by cesarean section,including 23 cases of macrosomia(≥4000g)and 13 cases of low-birth-weight infants(≤2500g).The birth weight ranged from 2180g to 4655g,with an average of(3570.52±492.75)g.There were linear correlations between BPD,HC,FL,AC,FTSTT,AVol,TVol and neonatal birth weight.The correlation coefficients(r)were 0.407,0.413,0.386,0.602,0.577,0.751,and 0.820,respectively(all P<0.001).There were also linear correlations characteristic between BPD,HC,FL,AC,FTSTT,AVol,TVol and neonatal SSFT.The correlation coefficients(r)were 0.446,0.448,0.493,0.587,0.516,0.637,and 0.766,respectively(all P<0.001).Stepwise multivariate linear regression analysis was performed with birth weight as dependent variable and BPD,HC,FL,AC,FTSTT and AVol,TVol as independent variables.According to the results of multivariate linear regression,the multivariate linear regression equation fitted with HC,AC,AVol,TVol as independent variable is Y=-2689.231+4.323X1+12.987X2+8.866X3+6.891X4.The adjusted R~2 was 0.786.It is shown that the fitted equation can reflect the original data very well.The test result of multivariate regression equation:F value was 51.377(P<0.001).Conclusion1.FLV parameters derived from three-dimensional ultrasound can reflect fetal subcutaneous fat better than conventional two-dimensional ultrasound parameters.2.FLV combined with conventional two-dimensional ultrasound parameters can provide a new method for prenatal estimation of fetal weight.3.FLV can provide new information for prenatal diagnosis of macrosomia and low-birth-weight infants.4.FLV measurement is simple and reproducible.It can be used as a routine biological index in clinical practice.