Objective: To compare excursion index of the septum primum (EISP) among Thai fetuses of gestational diabetic mothers (FGDMs) with and without septal hypertrophy (SH) and those of nondiabetic mothers from 32 to 35 weeks’ gestation.
Material and Method: Fetuses of Thai pregnant women were recruited for prenatal 2-dimensional echocardiographic measurements of the EISP (the ratio between the linear displacement of the flap valve of septum primum and the left atrial diameter) at 32 to 35 weeks’ gestation. All had confirmed gestational age and normal structural scanning. The EISP was compared among gestational age - matched 15 FGDMs with SH, 18 FGDMs with normal septal thickness, and 20 fetuses of nondiabetic mothers. The data were presented as mean and standard deviation (SD). Analysis of variance (ANOVA) was used to compare the EISP of the three groups.
Results: Fifty-three measurements were obtained. Comparison among the three groups showed that the mean and SD of the EISP were 0.27 + 0.04, 0.50 + 0.04 and 0.51 + 0.05 in FGDMs with SH, normal septal thickness and those of nondiabetic mothers, respectively. The analysis demonstrated that the EISP was significantly less than in FGDMs with SH when compared to the FGDMs with normal septal thickness and those of nondiabetic mothers (p < 0.01). There was no significant difference in the EISP of the FGDMs with normal septal thickness and those of nondiabetic mothers (p = 0.16).
Conclusion: Mobility of the septum primum in FGDMs with septal hypertrophy is reduced. This may indicate a higher preload compared to FGDMs with normal septal thickness and those of nondiabetic mothers.

Keywords: Fetal echocardiography, Left ventricular diastolic function, Gestational diabetes, Septum primum mobility, Excursion index, Septal hypertrophy