After the 2017 tournament, it was announced that tournament would expand to 10 teams for 2019, having been played with 8 teams since the first tournament in 1990, except in 2004, 2007, 2008, and 2009, where 9 teams played. The 2004 edition featured 9 teams when Japan was promoted from Division II but no team was relegated from the Top Division in 2003, due to the cancellation of the top division tournament in China because of the outbreak of the SARS disease. Two teams were relegated from the Top Division in 2004, going back to 8 teams for 2005, but due to the success of the 9-team pool in 2004, IIHF decided to expand again to 9 teams for 2007. IIHF reverted to 8 teams after the 2009 tournament, and play continued in this format until the expansion of 2019.