Value Of Fetal Pulmonary/Aortic Ratio Measured In The Short-axis View In The Second Trimester

Objective:To assess the normal fetal pulmonary, aortic inner diameters and pulmonary/aortic ratio at18-23weeks gestation and their changes in fetuses with cardiac outflow tract defects and other cardiac defects.Methods:6763unselected singleton pregnancies were enrolled from September2008to October2010. We performed our study on6699normal fetuses with gestational age ranging from18to23weeks and35cases of cardiac outflow tract defects,29cases of other cardiac defects at short-axis view of fetal echocardiography. Fetal pulmonary, aortic inner diameters and pulmonary/aortic ratio were measured when fetal excessive movements were avoided. Neonatal echocardiography was conducted within three days after birth. Postmortem was performed if pregnancy was terminated due to fetal abnormalities. Correlation analysis was calculated to determine the coeficient of correlation of the fetal pulmonary, aortic inner diameters and pulmonary/aortic ratio vs. gestational age (GA). Applying regression analysis to find the best-fit regression model and establish best-fit equations to obtain the predicted values of fetal pulmonary, aortic inner diameters respectively using GA as the independent variable. Then the goodness of fit of the regression model was assessed. To establish the chart of the normal reference centiles of fetal pulmonary, aortic inner diameters, the age-related reference centiles were calculated using the regression equation. To assess intraobserver reproducibility of diameters measurements, some fetal aortic and pulmonary diameters were measured three times consecutively by two observers at random. Meanwhile, fetal pulmonary, aortic inner diameters in fetuses with cardiac outflow tract defects and other cardiac defects are also measured by fetal echocardiography. Fetal pulmonary, aortic inner diameters in fetuses with cardiac defects are compared with that in normal fetuses using univariate general linear analysis model.Results:Paired t test showed no statistical significance for the intraobserver reproducibility. Our results showed that fetal pulmonary, aortic inner diameters are highly correlated with GA. Furthermore, the best-fit equation of fetal pulmonary, aortic inner diameters and GA was transformed into linear regression equation of which the residual showed homogeneity of variance and normal distribution. Following the theory of normal distribution, the age-related reference centiles was calculated and a normal growth chart of fetal pulmonary, aortic inner diameters and pulmonary/aortic ratio were established for clinical reference using GA as the independent variable and fetal pulmonary, aortic inner diameters as the dependent variable, the best-fit regression equation was Y(aortic inner diameter (cm))=-1.865+0.238X (GA)(r=0.373,p<0.0001) and Y(pulmonary inner diameter(cm))=-1.916+0.256X (GA)(r=0.357,p<0.0001). Corrected by GA, in fetuses with cardiac outflow tract defects, the fetal pulmonary inner diameter and pulmonary/aortic ratio were statistically different from that in normal fetus. While the fetal pulmonary, aortic inner diameters and pulmonary/aortic ratio in the status of other cardiac defects have no statistically difference than that in normal fetus.Conclusion:Our research established a normal growth chart of fetal pulmonary, aortic inner diameters and pulmonary/aortic ratio for clinical reference. In fetal with cardiac outflow tract defects, pulmonary/aortic ratio assessed by short-axis view of cardiography are statistically different from that of normal fetus.