sentence: According to the therapeutic strategies for PDA registered in the KNN database , we further stratified the sPDA group into the following two subgroups to compare the risk factors in the treatment and nonintervention groups that mediated sPDA closure : treated group ( sPDA_tx ) , comprising patients who had received any treatment for sPDA ; untreated group ( sPDA_nontx ) , comprising patients who had received only conservative treatment or no treatment for sPDA .