By Sweta Singh and Ankur Banerjee

(Reuters) - Last fall, Jessica Mah, the founder and chief executive of San Francisco-based inDinero, was deluged with calls from investors wanting to know when the accounting software maker would go public.

The conversation has changed dramatically since.

"My investors are now pushing for not wanting to go public anytime soon," said Mah, who started inDinero six years ago when she was 19.

The change in inDinero's investor sentiment reflects the uncertainty prevalent in the U.S. IPO market.

This year 39 companies have gone public so far, down more than 60 percent from the same period last year, according to data from Renaissance Capital, a manager of IPO-focused ETFs.

The pace of the market is unlikely to pick up, as declining valuations – a quarter of the IPOs this year are trading below their offer price – dampen investor appetite, and easy availability of private capital keeps companies satiated.

"Investors are more valuation sensitive today than they were in 2015," said Benjamin Howe, co-founder and CEO of AGC Partners, a Boston-based boutique investment bank.

The Renaissance IPO Index, a float-weighted index of U.S. IPO performance, has had negative returns of 7.2 percent so far this year, compared with positive returns of 2.2 percent for the S&P 500 index <.SPX>.

Howe said the IPO market has been "horrendous and I don't see that changing anytime soon."

There are also other factors for investors to consider: Britain's impending vote on its European Union membership, the upcoming U.S. presidential elections and the timing of an interest rate hike by the Federal Reserve.

TECH TONIC

Investors have also been skittish about the usually sought-after technology stocks, keeping at bay the so-called unicorns, or start-ups valued at more than $1 billion.

SecureWorks Corp <SCWX.O>, Dell Inc's cyber security unit, was one of the two tech companies to go public this year. The stock fizzled in its April debut and currently is flat with its IPO price.

The debut of communications software provider Twilio Inc on Thursday will help test the waters for other tech companies and unicorns in the coming months.

However, several IPO experts say even if Twilio has a stellar debut, that would unlikely rub off on the rest of the market.

Biotechnology companies – the biggest boost to the IPO market in terms of volumes last year - have also underperformed, plagued by increased scrutiny over drug pricing practices.

The Nasdaq Biotechnology Index <.NBI> has fallen nearly 25 percent this year and is on track for its worst half-yearly performance since 2002.

Of the 23 healthcare companies that have gone public this year, eight are trading at a discount to their offer price.

"When the stocks are not exceeding average S&P returns or trading below their IPO price, that causes people to back away from the market," said Richard Truesdall, co-head of global capital markets at law firm Davis Polk & Wardwell.

"There is enough uncertainty and clouds in the horizon that is causing people to be cautious."

(Reporting by Sweta Singh and Ankur Banerjee in Bengaluru; Editing by Sayantani Ghosh and Savio D'Souza)