Objective: To establish the normal value of fetal diastolic function by the measurement of the excursion index of the septum primum (EISP) from 32 to 35 weeks’ gestation in Thai fetuses.
Material and Method: Fetuses of normal Thai pregnant women were recruited for 2-dimensional echocardiographic measurements of the EISP (the ratio between the linear displacement of the flap valve and the left atrial diameter) from 32 to 35 weeks’ gestation. All had a confirmed gestational age, normal structural scanning, and negative diabetic screening at 24 to 28 weeks’ gestation. The 5th, 50th and 95th percentile of the EISP were demonstrated. The relationship between the EISP and gestational age were determined.
Results: Three hundred twenty-seven measurements were obtained. The normal values of the EISP according to gestational age were presented as 5th, 50th, and 95th percentile ranks. The correlation coefficients (r) between the EISP and gestational age were 0.03. The EISP were not statistically different with advancing gestation. The 5th, 50th, and 95th of the EISP were 0.32, 0.45, and 0.59 respectively. The intra-observer variability was 5.5%.
Conclusion: The normal values of fetal EISP in the Thai population from 32 to 35 weeks’ gestation were established. This could serve as a baseline data in detection of the alteration of left ventricular diastolic function during fetal life.

Keywords: Septum primum mobility, Diastolic function, Normal value, Fetal echocardiography, Excursion index