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.

Results:
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.

Conclusion:
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.

Keywords:
Fetal echocardiography, Nomogram, Superior vena cava

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