Value of Fetal Abdominal Subcutaneous Tissue Thickness by Ultrasound in Estimation of Birth Weight

Abstract

Assessment of fetal growth in-utero leads to improved management of high risk pregnancies. It is an independent factor to determine optimal survival of fetus; fetal weight is undoubtedly one of the most significant determinants of neonatal survival Ultrasound is the best technique to monitor fetal growth and estimate fetal weight. Subcutaneous fat thickness had a high degree of correlation with actual birth weight. Measurement of fetal subcutaneous fat by ultrasound is an attractive alternative to predict abnormalities in fetal growth. macrosomic fetuses had an increase in subcutaneous fat and vice versa. Recently, studies have shown that subcutaneous tissue thickness measurements, either on their own or incorporated into conventional fetal weight prediction formula could be used to evaluate fetal growth. The present study aimed to assess the reliability of fetal abdominal subcutaneous tissue thickness (FASTT) measured by ultrasound at term in prediction of birth weight. This study was prospective observational study conducted at fetal medicine unit of Ain-shams maternity hospital from November 2015 to September 2016. This study included 185 pregnant women with single viable fetus whom were seen for third trimestric ante-natal care within one week before prepared elective caesarean section at term (37-42) weeks of gestation or within one week before onset of spontaneous delivery. Multiple gestation, fetuses with congenital malformations, intrauterine fetal death and Oligohydraminos were excluded. Transabdominal ultrasound was done to measure the conventional fetal biometry including BPD, AC and FL and to measure the subcutaneous tissue thickness which is the area between the hyperechoic lines at the anterior one third of the abdominal circumference at the cut section showing stomach, hepatic veins. In the current study, the mean maternal age was 29.39±4.49 years and most common maternal age ranged between 26-30 years old, majority of cases were multipara delivered by cesarean section and the larger proportion of cases delivered female babies. In the present study there was significant positive correlation between maternal body mass index and both fetal abdominal subcutaneous tissue thickness and actual birth weight. In this study there was no statistically significant difference between mode of delivery or fetal gender and both fetal subcutaneous thickness and actual birth weight. In the present study, there was positive correlation between calculated fetal weight using hadlock formula and both abdominal subcutaneous tissue thickness and actual birth weight. Receiver operating characteristics (ROC) curve was used to define the best cut off value of calculated fetal weight for prediction of birth weight abnormality which was 3950gm for large birth weight (>90th), with sensitivity of 93.8% specificity of 93.8% diagnostic AUC of 99%, and was 2930gm for small birth weight (<10th) with sensitivity of 94.7% specificity of 92.8% and diagnostic AUC of 99%. In the current study there was positive significant correlation between subcutaneous tissue thickness and actual birth weight. Receiver operating characteristics (ROC) curve was used to define the best cut off value of fetal abdominal subcutaneous tissue thickness for prediction of birth weight abnormality which was 7.6mm for large birth weight (>90th) with sensitivity 89.5% of specificity of 93.9% with diagnostic AUC of 94.6% and was 4.9mm for small birth weight (<10th) with sensitivity 87.5% of specificity of 79.9% and diagnostic AUC of 91%.