The causes of patent ductus arteriosus are not known. However, we do know some risk factors for this condition. For instance, premature infants are more likely to develop a PDA than full-term infants: it occurs in slightly less than 1 percent of all premature infants, and about two of every 1,000 full-term babies. In addition, PDA is twice as common in girls than boys, and is more likely to appear in babies with neonatal respiratory distress syndrome. It is also common in babies with congenital heart problems, such as hypoplastic left heart syndrome, pulmonary stenosis and transposition of the great vessels. Infects with genetic disorders such as Down syndrome and those whose mothers have measles during pregnancy are at greater risk as well.