Futures Pare Gains on Earnings; GE, MCD Lower

U.S. stock index futures trimmed some gains Friday, with major averages poised to post their worst weekly declines this year, as investors reacted to the latest wave of earnings reports.

Markets were also unnerved by the news that the Boston Marathon bombing suspects - armed with explosives and guns - battled law enforcement officers in a Boston suburb early on Friday. One suspect remains at large, while the other was killed. Boston areas residents have been told to stay inside while police search for the suspect.

With no major economic news on tap Friday, the focus will remain largely on corporate earnings.

General Electric reported results that beat on profit and revenue, but weakness in the company's European operations dimmed optimism, sending shares lower in pre-market trading.

McDonald's edged lower after the fast-food chain missed earnings expectations by a penny and said global comparable sales were down 1 percent for the quarter, with China and Japan weakness helping drive sales in the Asia/Pacific, Middle East, and Africa (APMEA) region down 3.3 percent.

IBM tumbled after the computer hardware and software company posted quarterly results that fell short of consensus estimates and issued a full-year earnings forecast below estimates. In addition, the tech firm said it will accelerate the pace of job cuts after sales of software and mainframe computers slowed.

Next week, about 170 of the S&P 500 companies and 10 Dow stocks will report earnings, including industrial, consumer, pharmaceutical and energy companies.

"Earnings, I would argue are coming in better than expected. Underneath the surface is something that's not quite so healthy.They're struggling on the top line, the revenue side. That is indicative of a global economy growing below trend," said Bill Stone, chief investment strategist at PNC Wealth Management.

SeaWorld shares are expected to begin trading on the New York Stock Exchange under the symbol "SEAS" on Friday. The company priced its IPO at $27 per share on Thursday, at the high end of its expected range. (Read More: SeaWorld IPO Hopes to Make a Splash)

Vertex Pharmaceuticals skyrocketed after the drugmaker reported a successful trial for its experimental cystic fibrosis drug.

Meanwhile, GlaxoSmithKline traded lower after the pharmaceutical giant was accused of market abuse by the U.K.'s Office of Fair Trading on Friday. The regulator alleged that Glaxo paid generic firms to delay launching cheap copies of its top-selling anti-depressant Seroxat.

In Asia, shares traded higher on Friday after comments from China's central bank suggested a widening of the Yuan's trading band could be imminent.

European shares were also higher, boosted by gains in mining stocks after better-than-expected output numbers from Anglo-American.

The G20 (Group of 20) will wind down its two-day meeting in Washington on Friday, ahead of the Spring meetings of the International Monetary Fund (IMF) and the World Bank. Treasury Secretary Jacob Lew will speak before the IMF at 5:15 p.m. New York time.

(Read More: What the G20 Need toTalk About This Week)