By Kyle Alspach , Boston Business Journal

BOSTON (CBS) – The late summer and early fall had been shaping up as a prime season for initial public offerings of stock in the U.S. — a relief for mature private companies looking to complete the always-tricky process of going public, and for venture capitalists hoping to gain some badly-needed liquidity.

A dozen IPO’s were scheduled for the second week of August alone.

Only two made it out.

“The IPO market had been picking up momentum really for the last year,” said Ben Howe, CEO of Boston-based investment bank America’s Growth Capital.

“We had the potential for a very heavy IPO calendar based on what had been the trends of a strong stock market. But where we are right now, the markets are anything but stable.”

The gyrations in the stock market led Boston-based online backup firm Carbonite Inc. — one of the successful IPO companies during the week of Aug. 8 — to accept a 41 percent lower price for its shares than originally hoped for.

Meanwhile, the outcomes for the nine other Massachusetts-based companies that are registered for pending IPOs, and the many others whose owners are thinking about it, will now much be more uncertain.

“The IPO window is typically two years long,” said Fred Destin, a partner at Atlas Venture in Cambridge. “This one shut early.”

It doesn’t necessarily mean no companies will succeed at going public in coming months, though. Howe estimates 75 percent of companies currently registered will be able to complete the process this year.

But like Carbonite, they’ll likely have to accept lower valuations, he said. And they may also see less of a lift in price once the shares start trading compared to some of the recent IPO companies, such as Cambridge-based Zipcar Inc. and LinkedIn Corp., Howe said, whose firm has not underwritten an IPO this year.

Among the Bay State firms currently in IPO registration with the U.S. Securities and Exchange Commission, seven had filed since May as the IPO market gained steam.

They include Aspen Aerogels Inc., a Northborough-based producer of advanced insulation, which has RockPort Capital Partners of Boston among its backers; Demandware Inc., a Burlington e-commerce software firm, funded by North Bridge Venture Partners of Waltham and General Catalyst Partners of Cambridge; and Merrimack Pharmaceuticals Inc., a cancer therapeutics firm in Cambridge, which has backing from Boston-based Fidelity Investments.

Lisa van der Pool of the Boston Business Journal reports

The investors in those companies declined to comment or didn’t return messages about the status of the IPO plans.

As for companies working on filings to go public, they are more likely to rethink things, Howe said. “People that don’t have to get their companies public tend to shy away from being exposed to the types of markets that we saw last week,” he said.

Marketing an IPO to investors takes a large amount of money and management time for a company, and some companies won’t bother if there’s a risk they could get sub-optimal pricing or may even have to pull the deal, Howe said.