To investigate the characteristics of inferior vena cava compression syndrome in the second and third trimesters of pregnancy by echocardiography.

A total of 42 subjects at Beijing Baiziwan Hemei Women's and Children's Hospital from January 2016 to November 2018 [20 with symptoms of inferior vena cava compression (IVCC), 22 without IVCC symptoms] were recruited according to whether there were definite symptoms of IVCC in the second and third trimesters of pregnancy, and 14 age-matched subjects who did not have pregnancy were recruited as controls. The following parameters were recorded: left ventricular end diastolic diameter (LVEDD), left ventricular end systolic diameter (LVESD), left ventricular ejection fraction (LVEF), right ventricular basal dimension (RVBD), and pulmonary blood flow velocity. The peak flow velocity of the inferior vena cava was measured in the supine position, lateral position, and upright position, and the ratio of peak velocities in different positions was calculated. One-way analysis of variance (ANOVA) and Student's t-test with post hoc Bonferroni correction were used to compare continuous variables among the three groups and between two groups, respectively. The receiver operator characteristic (ROC) curve was used to analyze the ratio of inferior vena cava blood flow velocity and inferior vena cava blood flow velocity under different positions to predict the compression of inferior vena cava.

Compared with normal controls, the blood flow velocity of the inferior vena cava was significantly increased in the supine position and left lateral position in the pregnant group, and further increased in the symptomatic pregnant women group, and there was a significant difference in blood flow velocity of the inferior vena cava in the upright position among the three groups (P<0.05). In ROC curve analysis, inferior vena cava blood flow velocity>157.5 cm/s showed a 69% sensitivity and 23% specificity in predicting inferior vena cava compression. Additionally, the ratio of the velocity of the inferior vena cava in the supine position to that in the upright position>1.96 showed a 61% sensitivity and 83% specificity in predicting inferior vena cava compression.

Monitoring the flow velocity of the inferior vena cava and the ratio of the velocity of the inferior vena cava in the supine position to that in the upright position is of great clinical significance in predicting inferior vena cava compression in the second and third trimesters of pregnancy.