Clinical Significance of Fetal Subcutaneous Thickness via Ultrasonography Biometry in the Third Trimester for Estimating Fetal Birth Weight

Objective: In Korean population, information is lacking regarding fetal subcutaneous tissue thickness (SCTT) detected during pregnancy in the normal maternal condition. Thus, the aim of this study is to evaluate SCTT in the basic fetal biometry measurement plane, and to identify the clinical significance of SCTT in estimating fetal weight. Methods: In this retrospective observational study, 856 term pregnant women were recruited between 1st January 2013 and 31st December 2015. Estimated fetal weight (EFW) and fetal SCTT were measured routine ultrasonography within one week before delivery. The women were divided in two groups: SCTT group (n=46) and non-SCTT group (n=810). Pregnancy outcomes including birth weight (BW) and EFW were compared between the two groups. Results: The incidence of SCTT was 5.4% and no significant differences in parity, maternal age, maternal pre-pregnancy body mass index or gestational age at delivery were found between the groups. EFW, BW, amniotic fluid index, and cesarean section rate were higher in the SCTT group than in the non-SCTT group. The difference between EFW and BW was only significant in the SCTT group. Moreover, SCTT and EFW were positively correlated with BW (SCTT group: EFW 3,460±472 g vs. BW 3,779±496 g, P=0.013; non-SCTT group: EFW 3,011±436 g vs. BW 3,090±468 g, P=0.324). Conclusion: Fetal SCTT detected during routine biometric ultrasonography evaluation in the third trimester of pregnancy could suggest larger BW than EFW. Therefore, physicians should pay careful attention in such cases during assessments for delivery.