I was taking metformin for PCOS, during preop liquid diet, I had to stop because I was dropping my blood sugar. I had also started taking birth control about 3 months prior to surgery and the surgeon told me to stop because of an increased risk of blood clots after surgery. He said that I could restart in a couple of months. I was difficult for me to start the birth control with the side effects, then just to stop them. What I would suggest is "safe sex" until after surgery, then start the birth control.