Stock index futures pointed to a flat open on Thursday as the economy grew less than expected in the first quarter, adding evidence that global demand is slowing and underscoring recent equity weakness.

The S&P 500 is down 3.2 percent so far this month on concerns about global growth and foreign headwinds. Investors said Wednesday's rally, which broke a three-day losing streak, may not be enough to overcome macroeconomic worries.

Gross domestic product rose at an annual rate of 1.8 percent in the first quarter, unchanged from the previous estimate and down from analysts' expectations for more robust growth.

At the same time, new claims for initial jobless benefits unexpectedly rose last week.

This is disappointing data, but most people have been baking into their assumptions that this recovery won't be too robust, said Randy Bateman, chief investment officer of Huntington Asset Management in Columbus, Ohio, which oversees $14.5 billion. Because (the weakness) isn't too surprising, we shouldn't see too big of a reaction in stocks.

In a sign of rising concerns about the economic outlook, Goldman Sachs lowered its year-end target for the S&P to 1,450 from 1,500, citing margin concerns.

S&P 500 futures rose 1.7 points and were slightly under 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 18 points and Nasdaq 100 futures fell 4.5 points.

Hedge fund manager David Einhorn called for Steve Ballmer, the chief executive of Microsoft Corp , to step down. Shares of the Dow component rose 0.5 percent to $24.31 in premarket trading.

Tiffany & Co shares rose 4.2 percent to $73 in premarket trading after the luxury retailer reported its first-quarter results and raised its outlook.

Sony Corp's <6758.T> forecast of its first annual net profit in four years was viewed as optimistic, as the consumer electronics giant struggles with the aftermath of the March earthquake and a series of network security breaches.

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.

(Editing by Kenneth Barry)