Despite widely held expectations that the Federal Reserve's Federal Open Market Committee will continue reducing its bond-buying program on schedule, investors will be on guard for any surprises during the FOMC's announcement, while also closely tracking data on GDP, employment and PMI.

Futures on the Dow Jones Industrial Average were down 0.07 percent while futures on the S&P 500 were down 0.16 percent and those on the Nasdaq were down 0.34 percent. On Tuesday, the Dow ended the day up 0.53 percent while the S&P 500 rose 0.48 percent and the Nasdaq climbed 0.72 percent.

The Carlyle Group LP (NASDAQ:CG), Hyatt Hotels Corporation (NYSE:H), Jones Lang LaSalle Inc (NYSE:JLL), Revlon Inc (NYSE:REV), Shutterfly, Inc. (NASDAQ:SFLY), Time Warner Inc (NYSE:TWX) and Yelp Inc (NYSE:YELP) are among those scheduled to announce earnings Wednesday.

On the data front, the ADP private payroll employment report for April is due at 8:15 a.m. EDT while GDP numbers for the first quarter of 2014 are due at 8:30 a.m., and the Chicago Purchasing Managers' Index, or PMI, for April is due at 9:45 a.m.

At the FOMC's announcement at 2:00 p.m., the Fed is expected to leave policy rates unchanged and alter its asset-buying program as expected with yet another $10 billion reduction in bond purchases.

“We expect no fireworks at the April gathering,” Michelle Girard, chief U.S. economist at RBS, said in a research note, according to MarketWatch. 

In Europe, markets were mostly weak with the Stoxx Europe 600 index down 0.19 percent while the FTSE 100 was up 0.07 percent. Germany’s DAX-30 fell 0.07 percent while France's CAC-40 was down 0.34 percent.

In Asia, Japan's Nikkei-225 closed up 0.11 percent while Australia's S&P/ASX 200 inched up 0.05 percent. Hong Kong’s Hang Seng fell 1.42 percent and the Shanghai Composite gained 0.3 percent. South Korea’s Kospi fell 0.15 percent while India's BSE Sensex was down 0.22 percent.