* Merck quarterly profit tops estimate but revenue misses
* Twitter to report earnings after market close
* More U.S. companies beating earnings expectations
* Indexes up: Dow 0.6 pct, S&P 0.5 pct, Nasdaq 0.7 pct (Updates to afternoon, changes byline)
NEW YORK, April 29 (Reuters) - U.S. stocks rose on Tuesday, helped by upbeat results from companies including Merck & Co and Sprint, as well as more deal activity on the healthcare front.
Merck & Co 's shares jumped 2.9 percent to $58.35, giving the S&P 500 its biggest lift, after it reported stronger-than-expected results.
Also, Britain's Reckitt Benckiser Group Plc confirmed talks to buy Merck's consumer health business, the latest asset up for grabs in a wave of recent pharmaceutical deals.
"We've gone through a fair chunk of earnings and market participants kind of get the story at this juncture. On balance, with expectations having been lowered, earnings beats are coming in around 70 percent and most of the forward-looking statements have generally been pretty decent," said Mark Luschini, chief investment strategist at Janney Montgomery Scott in Philadelphia, which manages about $63 billion in assets.
First-quarter profit growth for S&P 500 companies is seen at 3.7 percent, based on actual results and estimates for companies yet to report, compared with a forecast for 2.1 percent growth at the beginning of the month, Thomson Reuters data showed.
The Dow Jones industrial average rose 91.86 points or 0.56 percent, to 16,540.6, the S&P 500 gained 8.35 points or 0.45 percent, to 1,877.78 and the Nasdaq Composite added 28.264 points or 0.69 percent, to 4,102.665.
Sprint Corp shares jumped 10.2 percent to $8.19 after the No. 3 U.S. mobile provider reported an increase in quarterly revenue, as expected, due to a new billing plan that lowered wireless expenses.
On the down side, Coach Inc reported a sharp drop in North American sales and the stock slumped 8.5 percent to $46.15.
Archer Daniels Midland Co were last down 3 percent at $43.03 after its first-quarter profit and sales missed Wall Street estimates.
The Fed's two-day policy meeting began on Tuesday, with the central bank expected to again scale back its monthly bond purchase program. Investors will also be eager to get any guidance on when it might raise interest rates.
Data suggested the economy continued to gain momentum after the winter lull. U.S. consumer confidence dipped in April but remained near a six-year high, while home prices rose in February.
Shares of Twitter, up 3.8 percent at $42.26, is due to report after the market close. (Additional reporting by Angela Moon; Editing by Bernadette Baum and Nick Zieminski)