I am a new nurse who just started working in OB. I had a patient on mag after she had a c section. We had to monitor her urine output every hour. My preceptor said that when the mag "starts working" she will begin to diurese and get rid of "all that fluid she is holding". So, my question...does magnesium somehow cause a reduction in urine output, and if so, why? And then, why should her output increase after she has been on the mag a while? I can't find the answer anywhere, not even from my preceptor!