Between 5% and 10% of those born with Turner syndrome have coarctation of the aorta, a congenital narrowing of the descending aorta, usually just distal to the origin of the left subclavian artery (the artery that branches off the arch of the aorta to the left arm) and opposite to the ductus arteriosus (termed "juxtaductal"). Estimates of the prevalence of this malformation in patients with Turner syndrome range from 6.9 to 12.5%. A coarctation of the aorta in a female is suggestive of Turner syndrome and suggests the need for further tests, such as a karyotype.