Fretful investors, alarmed by an uncertain economy, slammed shut the initial public offering window for venture-backed companies in the first quarter, according to a study released Tuesday.

Five venture-backed companies raised $282.7 million through March 31, 87 percent less than the $2.2 billion raised in the comparable 2007 quarter and 91 percent less than the $3 billion raised than in the fourth quarter of 2007.

The Exit Poll study by Thomson Financial and the National Venture Capital Association also found a steep decline in venture-backed mergers and acquisitions in the first quarter. The survey found 56 deals, 20 of which had a total disclosed value of $2.5 billion. That compared with 29 disclosed deals worth $4.5 billion in the first quarter of 2007 and 40 disclosed deals worth $8.4 billion in the fourth quarter.

Citing a "looming recession" that has chastened investors, Emily Mendell, NVCA vice president of strategic affairs, said that a continuation of current trends could divert investments away from startups.

"If this backup continues into the year, we are concerned that VC firms will have to hold on to companies that now must wait for more favorable market conditions," she said in an e-mail. "That means that dollars earmarked for new investment will have to go to unexpected follow-on rounds."

Four of the five venture-backed IPOs came from life sciences companies. All told, they raised $221 million in the first quarter, led by the $83 million IPO of IPC The Hospitalist Company, which coordinates care of hospital patients. Backers include Scale Venture Partners, Bessemer Venture Partners, Morgenthaler Ventures, and CB Health Ventures.

The first-quarter drought also is reflected in data from Renaissance Capital's IPOHome web site, which tallied 22 pricings of all types of IPOs for the first quarter versus 59 in the 2007 period. Though they still could be withdrawn, IPOs generally are priced shortly before they begin trading.

The quarter's lone information technology IPO was the $61.8 million debut of security management firm ArcSight, which is backed by Kleiner Perkins Caufield & Byers, Institutional Venture Partners, Integral Capital Partners, and In-Q-Tel, the CIA's venture arm.

The biggest disclosed M&A deal for the quarter was Dell's $1.4 billion acquisition of EqualLogic, a data-storage company.

Disclosure: Red Herring's investors include DCM, whose co-founder and General Partner Dixon Doll is chairman-elect of the NVCA.