Stock index futures edged higher on Wednesday, a day after the Dow and the S&P 500 indexes hit a new closing record, on expectations that the Federal Reserve’s monthly bond purchases of $85 billion will be extended into next year. On the earnings front, shares of General Motors rose 1.5 percent in premarket trading after the company posted better-than-expected quarterly profit, thanks to strength in its core North American market and a smaller-than-anticipated loss in Europe.