Gross domestic product grew at an even faster clip than was initially believed in the first quarter.

Real GDP growth was revised higher to 6.1% in the first quarter from a 5.6% preliminary result. The biggest contributors to the revision were in capital spending and exports, the Commerce Department said on Thursday. GDP is a key economic indicator, as it measures the rate at which the economy is growing.

"This was a larger-than-typical revision for the second update of the quarter," said Peter Kretzmer, a senior economist at Banc of America Securities, in a research note. "However, it still seems likely that growth slowed appreciably this quarter, as the inventory reversal waned and final sales lost some momentum, just as the Federal Open Market Committee pointed out in its statement yesterday."

Nonresidential fixed investment was revised upward to a 6.2% annualized decline from a previous 8.2% slump, as equipment and software spending was revised to a 0.1% gain from a 2.3% drop. That revision added approximately 0.25% to GDP, according to Kretzmer.

The trade deficit was revised to $434.5 billion from a previous $443.7 billion, which tacked on about 0.3% to GDP, Kretzmer said.

Most economists predict that GDP growth will slow considerably to around 2% in the second quarter. "The slowdown reflects weaker consumer spending growth and a slowing of the inventory reversal process," said Kretzmer. "We look for 3% to 4% GDP growth in the second half of the year."