Subcutaneous Fat Thickness in the Prediction of Birth Weight at Normal Term Pregnancy

Abstract

Our limited study showed that fetal abdominal subcutaneous tissue thickness can serve as a useful parameter for estimating fetal weight. The study included 400 pregnant women and conducted in Ain Shams Maternity Hospital. The mean fetal abdominal subcutaneous tissue thickness (FAST) was 6.35 ± 2.02 mm (range: 3.5 – 14.8 mm). Among all included women, there were no significant correlation between fetal anterior abdominal wall fat thickness and each of maternal age, parity and gestational age. There was a significant positive correlation between fetal anterior abdominal wall fat thickness and birth weight [r=0.480, p<0.001] There was a significant difference between women with different birth weight categories (average, low and macrosomia) regarding the mean value of FAST. The best cutoff value of FAST above which macrosomia is more likely was 7.1 mm [sensitivity 100%, specificity 81.12%, positive predictive value (PPV) 21.21%, negative predictive value (NPV) 100%, positive likelihood ration (LR+) 5.30, negative likelihood ratio (LR-) 0]. The best cutoff value of FAST below which low birth weight is more likely was 4.3 mm [sensitivity 87.50%, specificity 92.25%, PPV 41.18%, NPV 99.25%, LR+ 11.30, LR- 0.14]. The AUC for the FAST as predictor of macrosomia was larger than that for it as predictor of low birth weight, indicating that FAST is a better predictor for macrosomia than for low birth weight. EFW by Hadlock's Formula (BPD, FL, AC) had been evaluated during our study as being one of commonly used weight estimation formulas. At both birth weight extremities, It had lower sensitivity but higher specificity when compared to results obtained from FAST as a predictor of fetal weight. Being a simple measure obtained through 2D ultrasound in a standard plane gives it high applicability. It could be combined with weight estimation formulas as a method to increase its accuracy especially at birth weight extremities.