Superior vena cava diameters in normal Thai fetuses

Establish the normative data of fetal superior vena cava (SVC) diameters from 20 to 38 weeks' gestation in Thai fetuses.

Thai pregnant women with normal fetuses were enrolled for 2-dimensional echocardiographic measurements of SVC diameters. All women had good menstrual history and a confirmed gestational age with first or second trimester ultrasound. The SVC diameters were obtained in caval long-axis view in both systolic and diastolic periods. The measurements were plotted against gestational age. The best-fit regression equations were obtained. The 5th, 50th, and 95th percentile were then calculated for each gestational age.

Three hundred three measurements were obtained. Regression analysis demonstrated a linear correlation between SVC diameter and gestational age in both early ventricular systolic and end ventricular diastolic periods. The best-fit equations were SVC maximum diameter (mm) = -1.379 + 0.183GA (week), r = 0.889 (p < 0.001), SVC minimum diameter (mm) = -1.194 + 0.134GA (week), r = 0.826 (p < 0.001) at early systolic and end diastolic periods respectively. The calculated values of the SVC diameters across gestational age were presented as 5th, 50th, and 95th percentile.

SVC diameter increases linearly across gestational age in both ventricular systolic and diastolic periods. These could be a basis for assessment of fetuses with abnormal cardiovascular physiology such as hydrops fetalis and intrauterine growth restriction.