This is because the group - born between April 1952 and July 1953 - will qualify for the state pension before then, unlike men of exactly the same age.
The forthcoming pensions revolution will see all Britons of state pension age will get a 'flat-rate' pension worth £144 a week - as long as they have at least 35 years of National Insurance Contributions (NICs).
But around 430,000 women born in the early 1950s will miss out on the new deal. Instead, a woman born between April 1952 and July 1953 will typically receive a state pension of £127 per week.
That's a big drop over the course of a year, which is why the Department for Work and Pensions (DWP) research concluded: "It could have a significant impact on the state pension received over the course of a lifetime, in comparison to a man with an identical NICs record."
The figures have enraged many older women, especially as men born between the same dates will reach their state pension age of 65 after the changes come into effect in April 2017 and will therefore get the higher state pension of £144 a week.
Neil Duncan-Jordan, from the National Pensioners Convention, thinks they are right to be angry.
"There is a group of women who are being particularly disadvantaged by the Government's pension changes," he told the Daily Mail. "The goal posts keep on moving for them."
However, the DWP insists that the women affected by this issue will still be better off because they will get their state pension for between 15 months and three years longer than a man of the same age and this will mean up to an extra £20,000 in extra pension payments.
According to the Financial Times, Pensions Minister Steve Webb said: "Many of this group of women will be thousands of pounds better off by being able to draw their pension years before a man of the same age, and they would not thank us if we made them wait years longer for their pension."
The fact remains, however, that these women's weekly state pension payments will be lower for the rest of their lives.