J Med Assoc Thai 2008; 91 (7):974

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Superior Vena Cava Diameters in Normal Thai Fetuses
Sudjai D Mail, Uerpairojkit B

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

Material and Method:
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 95thpercentile 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 95thpercentile.

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.

Fetal echocardiography, Nomogram, Superior vena cava

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