U.S. online labor demand saw a modest increase in December after declines in October and November, said The Conference Board on Wednesday.

The Conference Board Experimental Help Wanted OnLine (HWOL) Index stood at 101.7 in December, up from 99.3 in the previous month.

The HWOL Index measures changes over time in advertised online job vacancies based on data collected in real-time from more than 28,000 different online job boards, reflecting monthly trends in employment opportunities across the United States.

Among occupation groups, computer, engineering and legal related ads experienced the fastest growth in the past 12 months, showed the report.

"Online job ads grew during 2017 and the first half of 2018 but then started to slow up through December. This supports our forecast of a moderate slowdown in 2019 GDP growth," said Gad Levanon, chief economist with The Conference Board.

"In periods of economic slowdown, the number of job ads tends to flatten or even moderately decline. HWOL trends suggest continued recruiting difficulties, with more people joining the labor force and faster wage growth," he added.

The Conference Board forecast in November that U.S. economic growth is likely to slow down in 2019 as the fiscal stimulus will have run its course and labor and capacity constraints become more apparent.

The projection of an economic slowdown was widely shared by many renowned institutions, including Bank of America (BofA) Merrill Lynch Global Research and Goldman Sachs.