* UnitedHealth profit falls
* Nokia drops in premarket after earnings
* Futures up: Dow 50 pts, S&P 6.1 pts, Nasdaq 12 pts
By Chuck Mikolajczak
NEW YORK, April 18 U.S. stock index futures advanced on Thursday, indicating the S&P 500 will rebound from a broad sell-off in the prior session ahead of data on the labor market and a fresh batch of corporate earnings reports.
Equities have been whipsawed in the past three sessions, with a 1 percent move in either direction in the S&P 500 each day this week, the first such streak of volatility for the index since the start of February.
Worries about global demand have sparked sell-offs in commodities, which in turn have led to weakness in equities. However, some equity investors continue to use any dips as a buying opportunity.
"I'm having a more and more difficult time making the bull case given what we are seeing around the globe from an economic standpoint," said Keith Bliss, senior vice-president at Cuttone & Co in New York.
"At the same time, the reason why you are seeing these gyrations in the market is you still have the sense from the 'buy the dip' crowd that as long as the Fed is there backstopping this they don't see real substantial downside risk."
Earnings are expected from 28 companies in the benchmark S&P index on Thursday, including Dow components Verizon Communications, Microsoft Corp and IBM.
Morgan Stanley reported a stronger-than-expected first-quarter profit of $958 million, compared with a year-earlier loss of $119 million, as its wealth management business grew, but shares slipped 0.8 percent to $21.30 in premarket trade.
UnitedHealth Group Inc, the largest U.S. health insurer, said its first-quarter profit had fallen, in part because of lower government payments for its private Medicare services and prescription plans for older Americans.
At 8:30 a.m. (1230 GMT), investors will eye weekly initial jobless claims data. Economists forecast a total of 350,000 new filings, compared with 346,000 in the prior week.
PepsiCo Inc reported better-than-expected quarterly earnings, as price increases helped margins and the company stood by its full-year forecast.
S&P 500 earnings are now expected to have risen 1.7 percent in the first quarter, up from the 1.5 percent estimate at the start of the month, based on actual results from 56 companies and estimates for the rest, according to Thomson Reuters data through Tuesday morning.
Of the 56 companies that have reported earnings, 66.1 percent have topped analyst expectations but only 48.2 percent have beaten revenue forecasts.
S&P 500 futures rose 6.1 points and were 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 gained 50 points, and Nasdaq 100 futures added 12 points.
Later in the session at 10 a.m.