What are the downsides to gastric byp surgery?

specifically what are the nutritional ramifications because I have read that B-vitamins and protein cannot be absorbed because of the portion of small intestine that is byped. Also, what happens if there is a pregancy? What happens to a developing fetus if the B-vitamins and protein is not accessible? What are other downsides to gastric byp surgery? I want to make the best informed decision and I am afraid that I am only hearing of the "up" sides of surgery or at best "sugar coated" negative sides to the surgery. I would like the most information anyone is able to give me! Thank you!