If one child is born with tetralogy of Fallot, the second child may not be born with tetralogy of Fallot. Tetralogy of Fallot is a polygenic disorder with a 2.5% risk of recurrence in the next pregnancy for one previous delivery of a child with tetralogy of Fallot, an 8% risk of recurrence in the next pregnancy for two previous deliveries of patients with tetralogy of Fallot, a 2.5% risk of recurrence if the mother is a patient with tetralogy of Fallot, and a 1.5% risk of recurrence if the father of the fetus is a patient with tetralogy of Fallot. Tetralogy of Fallot is an abnormality of ventricular cone development that includes four pathologic changes, ventricular septal defect, right ventricular outflow tract obstruction, aortic ride-through, and secondary right ventricular wall hypertrophy. 3-6% of Tetralogy of Fallot are combined with pulmonary valve agenesis, and 11%-34% of patients have a microdeletion of chromosome 22q11. The presence of tetralogy of Fallot in the first child does not necessarily lead to tetralogy of Fallot in the second child, and close labor and delivery testing is recommended if the mother has delivered a child with tetralogy of Fallot in the past.