Use of ultrasound fetal shoulder soft tissue thickness measurement in estimation of fetal weight

Aims Birth weight (BW) estimation with ultrasound is of great importance in delivery decision and management of complications of delivery. The aim was to evaluate the effect of femur, humerus, and clavicular soft tissue thickness on BW and developed a formula for proper estimation of fetal weight. Methods This prospective cohort study, included 231singleton pregnancies, with 34 and 42 weeks of gestation, delivered within 48 h after ultrasound examination. In addition to four biometric ultrasound measures, shoulder soft tissue thickness, thigh and arm soft tissue thickness were measured from outer margin of skin to outer margin of bone shaft by same investigator. Spearman correlation test was used to assess correlations between soft tissue thickness measurements and BW. Linear regression model was used and R-2 to test accuracy of the new formula. Results The mean humerus soft tissue thickness (HSTT) was 12 +/- 3.5 mm (6-23.9 mm), mean femur soft tissue thickness (FSTT) was 15.9 +/- 3.8 mm (7.3-32 mm), mean clavicular soft tissue thickness (CSTT) was 12.9 +/- 3.2 mm (7.3-24 mm). There was a low correlation between BW and FSTT (r = 0.21, p = 0.001) and CSTT (r = 0.18, p = 0.005). Best fit formula was Log (BW) = -5697 + 7.2 (HC) + 15.3 (AC) + 22.6 (FL) + 17 (CSTT), was significantly correlated with BW (R-2 = 0.60). Conclusion BW increased as the ultrasound shoulder soft tissue thickness increased. Adding soft tissue thickness measurements to fetal biometry is similar in terms of estimating fetal weight from the existing estimated fetal weight formula.