In the present retrospective cohort study, each chart was reviewed by one of three authors (GPM, BL or SLL) if they met the following inclusion criteria: admission to the neonatal intensive care unit (NICU) between January 1994 and December 2005, gestational age at birth of 23+0 to 26+6 weeks, and coded at discharge using International Statistical Classification of Diseases and Related Health Problems, 10th revision for the diagnosis of PDA. The Ottawa Hospital General Campus NICU (Ottawa, Ontario) is a 24-bed university-affiliated combined level 2 and 3 unit on the same university campus as the Children’s Hospital of Eastern Ontario NICU (Ottawa, Ontario), which is a 20-bed level 3 medical and surgical unit. Babies admitted into both NICUs are cared for by the same group of neonatologists. All PDA ligations in the region are performed at the Children’s Hospital of Eastern Ontario.Diagnosis of a PDA was made clinically and confirmed by an echocardiogram, although not always before an initial trial of medical treatment. For the purpose of the present study, and to promote consistency over the study time period, the PDA was deemed hemodynamically significant if the baby required ventilatory support such that extubation was prevented due to possible overcirculation from the PDA and/or the PDA had a diameter of >1.5 mm or was described as moderate to large on echocardiogram (on some reports, the size was only described qualitatively). Exclusion criteria were: incomplete record of PDA treatment, no echocardiographical confirmation of PDA, duct-dependent congenital heart disease, suspected or confirmed major congenital anomaly, or death within the first seven days of life. Visit the best pharmacy that thousands of international customers already chose to be their favorite one and see how easy it can be for you to get that cheap viagra pills in the amount required for your treatment spending a lot less money than otherwise.