To establish the normal range of fetal atrioventricular (AV) time intervals during the second and third trimesters assessed by three different pulsed-wave Doppler techniques [superior vena cava and ascending aorta (SVC/AAO) method, tissue Doppler imaging (TDI), and pulmonary artery and pulmonary vein (PA/PV) method and analyze the correlation of AV value with gestational age, fetal heart rate, and heart area.

From June to December 2019, 227 normal fetuses who underwent echocardiography at the Sir Run Run Shaw Hospital of Zhejiang University College of Medicine were selected. The gestational age was 16 to 41 weeks. They were divided into five groups according to gestational age. Pulsed-wave Doppler methods including SVC/AAO, TDI, and PA/PV were applied to measure AV, respectively. The measurement success rate and the normal range of AV values in different gestational weeks were obtained. Single-factor analysis of variance and multiple comparisons (LSD-t method) were used to analyze the differences in AV values obtained by different methods. Pearson correlation analysis was performed to examine the correlation of AV values with gestational age, fetal heart rate, and fetal heart area. Intraclass correlation coefficient (ICC) was used to evaluate the in-observer and inter-observer repeatability of each method.

All the three Doppler methods achieved a high measurement success rate: SVC/AAO, 94.58%; TDI, 100%; PA/PV, 95.83%. The normal range of AV values was: AV-SVC/AAO, (115.94±6.67) ms; AV-TDI, (117.69±6.43) ms; AV-PA/PV,(123.70±6.42 )ms; the difference between them was statistically significant (t=-2.843, -12.662, -9.819; P=0.005, ＜0.001, ＜0.001). All AV values were positively correlated with gestational age (r=0.677~0.680, P＜0.001) and fetal heart area (r=0.648~0.654, P＜0.001), but negatively correlated with fetal heart rate (r=-0.568~-0.581, P＜0.001). In-observer and inter-observer repeatability tests showed that the three Doppler methods had good repeatability (ICC＞0.80).

All the three Doppler methods are feasible and reproducible in measuring fetal heart AV values; normal fetal AV values in the second and third trimesters are affected by gestational age, fetal heart area, and fetal heart rate, and there are differences in AV values measured by different methods. Therefore, choosing an appropriate method to measure the fetal AV time and understanding the difference between the measured values by different methods are very important in clinical work and have very important significance.