Ductus arteriosus and fetal echocardiography: Implications for practice.

The ductus arteriosus (DA) is a crucial part of the fetal circulation, both in the normal fetus and in critical congenital heart disease (CHD). It allows shunting between the pulmonary and systemic circulations. In physiological prenatal conditions, the DA lets the majority of right ventricular output bypass the fluid-filled, high-resistance lungs. The DA can cause hemodynamic compromise in the fetus and neonate when constricted or absent (in isolation or in patients with CHD) and may lead to pre- or postnatal sequelae within other systems when forming part of a vascular ring. In CHD, the DA can be interrogated by fetal echocardiography to infer information regarding severity of pulmonary outflow tract obstruction, adequacy of the sub-pulmonary ventricle to supply pulmonary blood flow, and to predict the likelihood of atrial septum restriction in transposition of the great arteries. A good understanding of the DA is crucial for fetal cardiologists.