Stock index futures were little changed on Thursday as investors looked ahead to data that could shed light on the economy's health amid worries that global demand was slowing.

Equities have been pressured recently, with the S&P 500 down 3.2 percent so far this month. Investors said Wednesday's rally, which broke a three-day losing streak in stocks, may not be enough to overcome macroeconomic worries.

The preliminary estimate of first-quarter gross domestic product is due at 8:30 a.m. (1230 GMT) and is seen rising by 2.1 percent compared with the 1.8 percent rate previously estimated by the government.

Though the economy was seen expanding in the quarter despite sovereign debt woes, geopolitical tensions and natural disasters overseas, a weaker-than-expected reading could exacerbate concerns about global growth.

Weekly jobless claims are also on tap, with 400,000 initial claims expected, down from the 409,000 posted last week but still considered high.

S&P 500 futures rose 2.7 points and were slightly above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures added 21 points and Nasdaq 100 futures were flat.

Influential hedge fund manager David Einhorn called for Steve Ballmer, the chief executive of Microsoft Corp , to step down, saying the world's largest software company's leader is stuck in the past.

The Federal Reserve Bank of New York is investigating whether Goldman Sachs' mortgage servicing arm did not conduct proper reviews before denying borrowers the option to lower their payments under a government loan modification program.

Companies scheduled to report quarterly results include H.J. Heinz Co , Tiffany & Co and Big Lots Inc .

The CME Group , which this month raised the amount of money required to trade silver and oil in response to wild price swings, may bring down margins over time once the market volatility eases, a senior official said on Thursday.

The successive margin increases, cited as one of the triggers for the big commodities rout on May 5, contributed to a slide in silver prices since touching a record high of $49.51 an ounce on April 28.

(Editing by Kenneth Barry)