Northwestern Memorial Hospital confirmed Wednesday that it has laid off 230 employees over the last month as part of an effort to reduce its cost structure by a quarter by 2017. The Streeterville health system, which has about 7,000 employees, said in a statement that 52 of those who lost their positions have found new jobs, most at the hospital. It said several others are being considered for roughly 200 openings. A spokeswoman said the hospital has cut jobs each of the past several years after annual reviews of its operations conducted amid budget discussions.