Squad sizes would also be increased from 28 players to 30 following feedback from teams and players.
"We want to keep building the momentum, which is why we are introducing these changes to the format for the 2021 process," World Rugby chairman Bill Beaumont said. "By ensuring an even more competitive and exciting tournament in the future, women's rugby can continue to play an instrumental role in driving forward the development of the game and significantly broadening rugby's global fan base."
The 2017 competition had 45 million video views, and a total reach of more than 70 million throughout the five match days. More than 750,000 fans from 230 countries and territories also visited the official website www.rwcwomens.com, setting new records for engagement of the multi-language content for a Women's Rugby World Cup.
A statement released by World Rugby said in line with its Women's Plan 2017-25, World Rugby is determined to further the impact of its flagship women's tournament, with the format amendments expected to boost the experience for both players and fans.