Motorcyclists and cyclists ride on a street inside a newly developed residential quarter in Hanoi, Vietnam on May 7, 2013. Hoang Dinh Nam | AFP | Getty Images

Singapore, a major international financial hub, lost its crown as Southeast Asia's top grossing market for initial public offerings in 2018. It was brought down by Vietnam, which is often not top of mind for stock investors. In fact, the communist country is still considered a frontier market by major index providers, meaning it's thought to be less established and riskier than even emerging markets. Singapore, meanwhile, is classified as a developed market. But Singapore's fall this year had little to do with Vietnam's rise, experts noted. Instead, they said, the wealthy city-state's open economy means it's more affected by global developments and there were plenty of reasons for companies to hold back their listing plans in 2018. "In the second half of 2018, global trade wars, political tensions and volatile markets have inadvertently impacted economic sentiments, causing delays in the listing timeline of some IPO aspirants," Tay Hwee Ling, Deloitte Southeast Asia and Singapore's global International Financial Reporting Standards and offerings services leader, told CNBC in an email.

Singapore's lackluster performance in 2018 is also in line with a fall in IPO activity worldwide as companies held back expansion plans amid the uncertain economic and geopolitical outlook. Singapore finished the year with 13 deals that raised around $500 million — the fourth highest IPO proceeds in Southeast Asia behind Vietnam, Thailand and Indonesia, according to data from consultancy EY. Vietnam, which was far behind its larger neighbors just two years ago, leaped to the top in 2018 with five IPOs raising $2.6 billion, EY said. Large IPO deals in the country came about after the government pushed ahead with a long-awaited privatization drive. The $1.35 billion IPO by real estate firm Vinhomes was the largest ever in the country and was Southeast Asia's second-biggest of 2018.

The changing landscape

With the Vietnamese government expected to sell its stake in more companies, the country could very well remain at the top of Southeast Asia's IPO league, according to a report from Baker McKenzie and Oxford Economics. The law firm and the consultancy projected earlier this month that the frontier economy would raise the largest amount of IPO funds in Southeast Asia through 2021, with Singapore and Thailand close behind.