The Washington-based organisation said global growth would weaken from 3.7% in 2018 to 3.5% this year, down 0.2 percentage points from its prediction last October.
She said the update projects global growth at 3.5 per cent in 2019, a downward revision of 0.2 per cent from the October report, and 3.6 per cent in 2020, a reduction of 0.1 per cent.
If there is a disruptive exit, or there is continued uncertainty for many more months, 'both of those are going to weigh negatively on growth going forward, ' she said.
"Efforts by policymakers to stimulate economic activity, such as cutting the required reserve ratio in the banking sector and broad tax cuts, have likely acted to prevent a more dramatic decline", he said in a note to clients.
Data released on Monday showed China's economy cooled in the fourth quarter on faltering domestic demand and bruising US tariffs, dragging 2018 growth to the lowest in almost three decades.
For 2020, growth projections were raised by 0.1% to 1.6% on the assumption that Britain will reach a Brexit deal this year and that the country will gradually transition a new regime.
The global growth forecast for 2020 is 3.6 percent, 0.1 percentage point lower than previously forecast.
The IMF sees the United Kingdom economy expanding 1.6 per cent in 2020, little changed from the 1.5 per cent it forecast in October.
The global lender also cited a bigger-than-expected slowdown in China's economy and a possible "No Deal" Brexit as risks to its outlook, saying these could worsen market turbulence.
After two years of solid expansion, the world economy is growing more slowly than expected and risks are rising.
Chinese growth helped kickstart the world's economy after the 2008 financial crisis and economists fear the slowdown will put a drag on global growth.
The main policy priority is for countries "to resolve cooperatively and quickly their trade disagreements and the resulting policy uncertainty, rather than raising harmful barriers further and destabilizing an already slowing global economy".
But it is in line with the World Bank's estimate of 7.3 per cent. Under President Donald Trump, the USA has imposed import taxes on steel, aluminum and hundreds of Chinese products, drawing retaliation from China and other US trading partners.
On Monday China announced that its official economic growth came in at 6.6 percent in 2018 - the slowest pace in three decades.
As the debts roll over, those borrowers have to refinance at higher rates.