A study by City, University of London showed that a recent upward trend in the numbers of women experts appearing on news programmes had plateaued.
Comparisons with an earlier study by City showed a rise of 29 per cent in women experts on the news since 2016.
However, researchers said almost all of this improvement occurred in 2017, with little change in 2018.
Professor Lis Howell, director of broadcasting at City, surveyed five weekday episodes of the flagship news programmes produced by the leading UK broadcasters - BBC, ITV, Channel 4, Channel 5 and Sky – for one week in every month over a two-year period.
The research showed that BBC News at Ten fielded fewer women experts in the second year of the study – between 2017/18 – than in the first.
The study said the overall improvement in the number of women experts appearing on the news was fractional, suggesting initial improvements had stalled.
Experts were considered to be anyone interviewed because of their expertise, influence or authority, including politicians, sports people and celebrities.
Howell presented her findings at the 2018 Women on Air conference yesterday.
Commenting on the findings, she said: "The two biggest programmes still have a lower number of female experts than the level of female expertise in society, which is around 2.5:1. ITV News at Ten has a ratio of 2.5:1 and BBC News at Ten has a ratio of 3:1."
Comparing broadcasters, Howell said ITV News at Ten – despite having a disproportionate number of male experts – had improved by 31 per cent since 2015/16, while the BBC News at Ten had improved by 18 per cent.
Howell said both broadcasters had work to do before achieving a ratio of fewer than 2.5 men to every woman expert.
"Channel 4 and Channel 5 perform best here," she added.
Reporters, correspondents and presenters
The study also looked at the proportion of women and men who were reporters or correspondents on the flagship programmes and found there had been an average improvement of 1.5:1 in favour of men, from 2:1 in 2015/16.
Within individual broadcasters, ITV News at Ten had stalled, remaining at 2.6 men to every woman and BBC News at Ten had slipped slightly to 2.3 men to every woman, from 2.1 in 2015/16.
The study also found ITV News at Ten has eight times more male presenter-led programmes than those led by a women, and BBC Radio 4 had twice as many male presenter appearances as female.
Channel 4 News also has twice as many male presenter appearances as female presenter appearances.
Howell said no broadcaster could claim "parity or near parity" across the three areas of the study.
In a letter to FTSE 100 chairmen yesterday, Kerry Hopkins, chief executive of not-for-profit the Broadcast Ready Club, cited the new research and invited them to take part in a campaign to add to their number of women spokespeople by offering media training.