To quantitatively analyze the variations of the post-left atrium space (PLAS) and post-left atrium space index (PLASI) in normal fetuses during the mid-to-late gestational period and fetuses with absent pulmonary valve syndrome (APVS), and to explore the application value of PLAS and PLASI in APVS fetuses.

A retrospective analysis was conducted on 20 fetuses diagnosed with APVS at Sir Run Run Shaw Hospital, Zhejiang University College of Medicine from October 2011 to September 2023, as well as 261 normal fetuses consecutively examined between February 2021 and February 2023. Measurements of PLAS and the diameter of the descending aorta (DA) were obtained in the four-chamber view, and PLASI was calculated. PLAS, DA diameter, and PLASI were compared between the control group and the APVS group. Receiver operating characteristic (ROC) curve analysis was performed to assess the diagnostic efficacy of PLAS and PLASI for APVS. Additionally, the relationships between PLAS, DA diameter, PLASI, and gestational age (GA) in both the control and APVS groups were examined. Furthermore, the characteristic ultrasound features of fetuses in the APVS group and their correlations with PLAS and PLASI were analyzed.

Compared with the control group, the APVS group exhibited significantly higher PLAS and PLASI values [(4.74±1.38) mm vs (2.70±0.62) mm and 1.225±0.210 vs 0.659±0.111, respectively, P<0.0001 for both]. ROC curve analysis indicated that the area under the ROC curve of PLAS was 0.958. When PLAS >3.3 mm was used as the cutoff point, the sensitivity and specificity of PLAS in distinguishing APVS from normal fetuses were 90% and 85%, respectively. The area under the ROC curve of PLASI was 1.000, When PLASI >0.93 was used as the cutoff point, the sensitivity and specificity of PLASI in distinguishing APVS from normal fetuses were 100% and 99.2%, respectively. In the control group, PLAS was positively correlated with GA (r=0.5495, P<0.0001), as was the DA diameter (r=0.6327, P<0.0001). In the APVS group, neither PLAS nor DA diameter showed a significant correlation with GA (P>0.05 for both). PLASI was not significantly correlated with GA in either the control group or the APVS group (P=0.127 and 0.1008, respectively). PLAS showed no significant association with the diameter of the main pulmonary artery (MPA) (P=0.2255), but exhibited a positive correlation with the cardiac axis (r=0.5140, P=0.0204). PLASI was not significantly correlated with either MPA diameter or the cardiac axis (P=0.2180 and 0.1299, respectively).

In APVS fetuses, PLAS loses its normal pattern, and both PLAS and PLASI are significantly higher than those in normal fetuses. Considering both sensitivity and specificity, when PLAS>3.3 mm and 1.0>PLASI >0.93 are used as the cutoff points, PLAS and PLASI can serve as effective assistant indicators for predicting APVS.