US Markets

US stock futures trim gains after release of Yellen testimony

U.S. stock-index futures reduced their gains on Tuesday as prepared testimony from Federal Reserve Chair Janet Yellen had Ben Bernanke's replacement stressing continuity in the central bank's approach to monetary policy.

"Bottom line, 'continuity' is what she said in her statement and that seems to be exactly what we got as her testimony was very similar to the last FOMC statement," Peter Boockvar, chief market analyst at the Lindsey Group, wrote in emailed research.

"We await the Q&A," he added.

Prepared remarks from Yellen – who took over from Ben Bernanke a little more than a week ago – were released ahead of her formal semi-annual policy report, expected at 10 a.m. Eastern, and comes on the heel of two weak monthly jobs reports in a row and a spate of market volatility largely tied to uncertainty in emerging markets.

(Read more: Tuesday's trade will be all about Janet Yellen)

"Continuity from Bernanke's leadership seems highly likely to be the overall impression left by today's testimony, with an emphasis on labor market developments in the round as key to the future direction of monetary policy," said Grant Lewis, head of research at Daiwa Capital Markets Europe, in a morning research note.

Immediately after Yellen, the House Financial Services Committee will hear reactions to her comments from Stanford University Professor John Taylor, the Cato Institute's Mark Calabria, the American Enterprise Institute's Abby McCloskey and former Fed Vice Chair Don Kohn.

Yellen to 'play it safe' for Congress: Pro

"We expect questions on the pace of stimulus reduction as well as exit measures, but do not expect Yellen to say anything beyond what the Fed has already communicated. Rather, we would focus on how upbeat (or not) her assessment of the U.S. economy is," said analysts at Mizuho Financial in a note.

Economic data due on Tuesday include wholesales sales and inventories for December at 3 p.m.

Apple stock will also be in focus Tuesday, after the tech giant lost its latest bid to put a court-appointed antitrust monitor on hold. Frankfurt-listed Apple shares traded around 0.4 percent higher during early European trade.

(Track: European markets with CNBC)

In addition, Google struck a major advertising deal with comScore on Monday, which could help the company win more business from big brands like Kellogg's. Google shares held steady on the Frankfurt stock exchange early on Tuesday.

—By CNBC's Katy Barnato