Many women may disagree, but the pain of passing a kidney stone - they usually get shoved out through the narrow urinary tract - has often been compared to the pain of childbirth. Kidney stones are formed when the concentration of minerals and substances like calcium oxalate, phosphate, oxalic acid and uric acid are too high in the urine. These then break out of the urine and begin to pack onto each other, or crystallise, in the kidneys, becoming what are known as kidney stones. Some stones are as small as a grain of sand, others the size of golf balls or even, in extreme cases, a hand-sized...