"We've got an inventory drain. The way the numbers are adding up is pretty much around the 1 percent range. It's weather related losses," said Diane Swonk, chief economist at Mesirow Financia, before the number was released. "We had a lot of disruptions. We didn't get the improvement in car sales until March. They were pretty weak in February. A lot of consumer-related weakness was related to the weather."
The change in private inventories subtracted 0.6 percent from growth, potentially a positive for the second quarter as businesses increase output to meet demand. Business spending fell at a 2.1 percent pace in the first quarter, the first decline in a year and a disappointment after the fourth quarter's 5.7 percent gain.
Swonk expected a pickup in health care spending, as more consumers spent on premiums for Affordable Care Act health care policies. That did show up in the number, with consumer spending gaining 3 percent and it was largely driven by health care and spending on utilities.
Maki had expected the inventory slowdown to be smaller than others forecast, and he had forecast 2 percent GDP for first quarter. "The final sales part, the consumption part should be the most important regardless of whatever the headline number prints," he said.
Maki forecast second quarter growth at 3 percent, though Swonk, with the weaker 1 percent first quarter forecast, expects it to jump to 3.8 percent. "This is a big roller coaster ride," she said. Fourth quarter growth was 2.6 percent.
Read MoreWhat the Fed will dothis week—and why it matters
LPL Financial strategist John Canally said he doesn't expect much from the Fed since it has no press briefing following the meeting.
"There's so much work to be done on that statement that they're not likely to spring it on us at a meeting where they have no other communication," he said.
"The Fed is not too worried about inflation and not too happy with job growth. If they continue to say that, the market is not going to care much," he said. "I don't think they can afford to make another misstep." He was referencing a comment made by Fed Chair Janet Yellen at her first press briefing about when the Fed could begin to raise rates. The markets took her remark to suggest that the Fed could raise rates six months after it ends quantitative easing literally, and Fed officials have spent a lot of effort to change that view.
Market focus Wednesday will also be on earnings, after Twitter's wider loss and 10 percent stock decline Tuesday. Dozens of earnings are expected before the bell, including Time Warner, GlaxoSmithKline, Royal Dutch Shell, Daimler, Thomson Reuters, WellPoint Health, Carlyle Group, Pitney Bowes, Sealed Air, Total, Exelon, Hess, Actavis, International Paper, and MeadWestvaco.
After the bell reports are expected from Boston Beer, Yelp, Shutterfly, MetLife, Williams Cos, Weight Watchers, WebMD Health, Flextronics, Cabot, Curtiss-Wright, Pilgrim's Pride, Terex, Ternium, JDS Uniphase, General Cable, Tesoro Logistics and Tesoro.
—By CNBC's Patti Domm. Follow her on Twitter @pattidomm.