Ventricular-arterial disproportion is a frequent observation in late gestation and mostly considered physiological. It is also an indirect prenatal sign for postnatal coarctation.

To investigate the remnant risk for coarctation and its possible risk factors in a fetal population with physiological late gestation asymmetry.

This was a monocentric, retrospective study conducted from 2014 till 2017 in a Fetal Cardiology Unit. All foetuses referred for third trimester asymmetry with pulmonary artery/aorta ratio>1.2 were included. Annular sizes, arterial Z-scores, valve ratios, isthmus size if available and minor associated cardiac defects were analyzed.

One hundred and one foetuses were referred at a mean gestational age of 33.5 SA. After foetal echocardiography, 2% (3/151) were considered at high risk for coarctation because of a hypoplastic arch and/or a small left outflow tract or isthmus. They were scheduled to deliver in a tertiary referral center. Two of these three newborns developed coarctation. In 98% of foetuses, asymmetry was considered physiological with a normally sized aortic arch without the “shelf sign”. All infants had an early ambulatory echocardiography that revealed coarctation in 7/148 cases (4.7%). There were no significant differences in mean arterial annular sizes, aortic and pulmonary Z-scores, pulmonary artery/aorta ratio, atrioventricular annular sizes, tricuspid/mitral valve ratio, presence of ventricular septal defect or left persisting superior caval vein between the two groups.

Remnant risk for coarctation in a foetal population with physiological late gestation asymmetry is<5%. Prenatal counselling can be reassuring since the majority of infants will have a normal heart. However early cardiac evaluation of these newborns remains recommended to exclude the rare event of postnatal coarctation in absence of prenatal predictive signs.