The Fed is expected to maintain its accommodative monetary policy, but investors will be looking for hints on when the central bank might start scaling back its monthly bond-buying program. Chairman Ben Bernanke will issue a statement at 2 p.m. ET, after the meeting ends.
"Given that expectations of a gradual tapering of stimulus prompted a downward spiral in May, it is no surprise that investors are anxious and will be looking for some reassurance and consistency in the Fed's message on monetary policy," said Andy McLevey, head of dealing at stockbroker Interactive Investor.
Facebook briefly poked above its May 2012 initial public offering price of $38 a share in pre-market trading, fueled by positive momentum following the company's better-than-expected earnings and a new program aimed at helping small and mid-size developers distribute their games.
Among earnings, Comcast rallied after the cable company posted quarterly results that exceeded Wall Street forecasts as it added more Internet customers than expected and saw a more than 20 percent increase in operating cash flow at its NBCUniversal unit. Comcast is the parent company of NBCUniversal.
MasterCard jumped after the credit-card provider beat earnings expectations. Rival Visa also traded higher.
Humana gained after the health insurance provider beat earnings expectations and lifted its guidance for the year on strong growth in membership levels.
And SodaStream zipped higher after the home soda systems maker topped earnings expectations.
Approximately 60 percent of S&P 500 companies have posted quarterly results so far, with 67 percent of firms exceeding earnings expectations and about 55 topping revenue estimates, according to the latest data from Thomson Reuters.
Allstate, CBS, Wholefoods and Dreamworks Animation are among notable companies slated to post results after the closing bell.
Air Products and Chemicals surged after activist investor Bill Ackman launched his biggest bet yet, taking a 9.8 percent stake in the company, a $2.2 billion investment.
Asian and European shares were mixed ahead of the Fed announcement. The Japanese Nikkei widened losses as dollar-yen fell below the 98-handle in afternoon trade on Wednesday, as investors digested the latest batch of corporate earnings. The Nikkei has been steadily declining since hitting a two-month high at 14,953 points on July 19.