Gold edged up on Thursday, extending gains to a third session, as hopes of more stimulus measures from central banks to revive a flagging global economy boosted bullion's appeal as a hedge against inflation. Spot gold inched up 0.1 percent to $1,605.89 an ounce by 0646 GMT, after rallying to a three-week top of $1,609.91 on Wednesday when it notched up its biggest daily percentage rise in about a month.