To determine the normal reference ranges of multiple parameters such as posterior left atrial space index (PLASI) and PLASI Z-score in normal fetuses from 16 to 40 weeks of gestation and assess their correlation with fetal biological growth parameters.

A total of 402 singleton fetuses with gestational age between 16 and 40 weeks were prospectively selected from July to December 2022 at the Affiliated Sir Run Run Shaw Hospital, Zhejiang University School of Medicine. Fetal biometric growth parameters including biparietal diameter (BPD), femur length (FL), and gestational age (GA) were obtained. End-diastolic width of the posterior left atrial space (LA-DAO-2DD, LA-DAO-MMD), end-systolic width of the posterior left atrial space (LA-DAO-2DS, LA-DAO-MMS), end-diastolic internal diameter of the descending aorta (DAOd-2DD, DAOd-MMD), and end-systolic internal diameter of the descending aorta (DAOd-2DS, DAOd-MMS) were measured by two-dimensional (2D) and M-mode echocardiography on the standard four-chamber views of fetal echocardiography, respectively. The posterior left atrial space end-diastolic index (PLASI-2DD, PLASI-MMD) and the posterior left atrial space end-systolic index (PLASI-2DS, PLASI-MMS) were calculated, respectively. BPD, FL, and GA were taken as independent variables, and the actual cardiac values of each measurement were taken as response variables. And regression analysis was applied to construct the best model, and the residuals (the difference between the actual measured values and the predicted values calculated from the equations) were calculated and analyzed. Then, the standard deviation (SD) was adjusted using absolute residual-weighted regression to determine the SD of the change in residuals relative to the independent variable falling within the normal range. According to the regression equation, the corresponding Z scores were calculated.

LA-DAO-2DD, LA-DAO-2DS, LA-DAO-MMD, LA-DAO-MMS, DAOd-2DD, DAOd-2DS, DAOd-MMD, and DAOd-MMS in normal fetuses were significantly correlated with increasing GA, BPD, and FL. Among them, the correlation of DAOd-2DS and DAO-MMS with GA was the best in two-dimensional and M-mode echocardiography (r=0.874 and 0.858, respectively; P<0.001 for both). PLASI-2DS and PLASI-MMS had no significant correlation with GA, BPD, or FL. PLASI-MMD showed a negative correlation with GA, BPD, and FL (GA and PLASI-2DD: r=-0.228, P<0.001; GA and PLASI-MMD: r=-0.121, P=0.016; BPD and PLASI-2DD: r=-0.246, P<0.001; BPD and PLASI-MMD: r=-0.135, P=0.007; FL and PLASI-2DD: r=-0.223, P<0.001; FL and PLASI-MMD: r=-0.128, P=0.010). The SD of LA-DAO-MMS and PLASI-MMD showed a simple linear relationship with their respective variables (GA and LA-DAO-MMS: r=0.120, P=0.016; GA and PLASI-MMD: r=-0.158, P=0.002; BPD and LA-DAO-MMS: r=0.136, P=0.006; BPD and PLASI-MMD: r=-0.159, P=0.001; FL and LA-DAO-MMS: r=0.136, P=0.006; FL and PLASI-MMD: r=-0.163, P=0.001). The Z-score values of DAOd-2DS, DAOd-2DD, LA-DAO-2DS, LA-DAO-2DD, DAOd-MMS, DAOd-MMD, LA-DAO-MMS, and LA-DAO-MMD remained relatively constant with the growth of GA, BPD, and FL (P>0.05 for all).

This study has established the normal range of PLASI and PLASIZ scores for normal fetuses between 16 to 40 weeks of gestation, and determined their correlation with GA, BPD, and FL.