Evaluation of the post-LA space index in the normal fetus

We previously reported the post-LA space index (PLAS index), which is calculated as left atrial-descending aorta distance (LD) divided by the diameter of descending aorta (DA), could be useful for prenatal diagnosis of total anomalous pulmonary venous connection (TAPVC). In this study, we evaluated PLAS index in normal fetuses to assess its usefulness.

In 304 normal fetuses, LD and DA were retrospectively measured, and the PLAS index was calculated. In 206 fetuses with data on the biparietal diameter (BPD) and femoral length (FL), the relationship between the PLAS index and them was investigated. We also calculated the PLAS index in 13 TAPVC fetuses.

Mean LD was 3.0+/-0.94 mm, mean DA was 4.8+/-0.87 mm, and the mean PLAS index was 0.62+/-0.19. DA and LD were correlated with gestational age (R = 0.52, 0.25), while the PLAS index showed little variation with gestational age (R < 0.2). BPD and FL were correlated with DA (R = 0.4, 0.42) but not with LD or the PLAS index (both R < 0.2). In the TAPVC fetuses, both LD and the PLAS index were significantly higher than in normal fetuses.

In normal fetuses, the PLAS index was independent of gestational age and fetal physique and may be useful for raising the suspicion of congenital heart disease, including TAPVC.