Stock index futures pointed to a lower open on Friday as investors found few reasons to buy following a volatile week and ahead of a speech from Federal Reserve Chairman Ben Bernanke on the economy.

Futures added to early losses after a weak reading on gross domestic product, which showed the economy grew much slower than previously thought in the second quarter -- an anemic 1 percent, revised down from a prior estimate of 1.3 percent.

The data followed a week where stocks gained early on as investors wagered the Fed could announce a new program to combat softness in the economy. That contributed to a three-day rally on the S&P.

For three straight days, the S&P has moved more than 1 percent. On Thursday, it fell as investors hedged themselves against Bernanke's speech, as well as on continued concerns about the U.S. labor market and the state of the European economy.

Most analysts believe Bernanke, scheduled to speak on Friday at 10 a.m. EDT, is most likely to outline gradualist measures -- disappointing those looking for a more dramatic move, such as a fresh round of asset purchases.

The GDP data was ugly but not a disaster, said William Larkin, portfolio manager with Cabot Money Management in Salem, Massachusetts. Had it been under 1 percent we'd have had more of a psychological reaction.

Larkin added that investors remained focused on the Bernanke speech. They really want something to come out of the meeting, but they're no longer expecting the kind of plan they were earlier this week.

While uncertainty about what the Fed will do has driven the recent volatility, many investors expect that volatility to subside after his comments.

S&P 500 futures fell 7.8 points and were below 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 fell 61 points, and Nasdaq 100 futures lost 11.5 points.

The Dow is up 3.1 percent for the week, while the Nasdaq is up 3.3 percent and the CBOE Volatility index <.VIX> is down 7.6 percent. The S&P is up 3.2 percent, but it remains to be seen whether stocks can gather enough steam for an extended rally. Analysts view 1,120 as a key support level for the index.

Futures continued to take cues from overseas. In Europe, shares <.FTEU3> fell 1.9 percent on nervousness ahead of Bernanke's speech.

A final reading on August U.S. consumer sentiment is also on tap and an index is seen rising to 56 from 54.9 in the preliminary report. The report comes at 9:55 a.m. EDT.

Financials will be the most reactive sector to Bernanke today, positively or negatively, since they've been at the center of the recent storm, Coleman said. They're the bellwether to watch.

Tiffany & Co rose 4.2 percent to $65.75 in premarket trading after it raised its full-year outlook.

Trading may be affected as Hurricane Irene is expected to barrel up the U.S. East Coast.

(Editing by Jeffrey Benkoe)