A new report said the gap between the hourly earnings of the two sexes widens after women become mothers.
Their hourly pay rate falls 33% behind men's over a 12-year period, it added.
But in Northern Ireland, there is an established trend of women earning more than men.
In 2010, typical (median) female full-time hourly earnings, excluding overtime, in Northern Ireland moved slightly ahead of male earnings for the first time.
That has continued over the last five years, except for 2012 when typical female and male full-time hourly earnings were the same.
In 2015, typical female full-time hourly earnings, excluding overtime, were 101% of male earnings compared to a ratio of 91% for the UK as a whole.
The pattern of women earning slightly more than men is not uniform across the income distribution.
Men have higher earnings in the 90th percentile (among the top 10% of earners), and at the 40th percentile and below.
The Office for National Statistics (ONS) has suggested that the gap in favour of full-time female workers overall is partly to do with a higher proportion of public sector jobs in Northern Ireland than in the rest of the UK.
There are more women employed in this sector than men and these jobs tend to be higher paid, in general, than in the private sector.
At a wider, all-employee level, there is still a gap in favour of men because there are more full-time male employees.
All of the above data is from the Annual Survey of Hours and Earnings.

Crystalla Dean, 52, was last seen by her daughter at her home in Longsdale Crescent, Oban, at about 20:00 on 15 December.
On 5 January a body was found on the shore at Ardmucknish Bay near Benderloch.
Police said the body had now been formally identified as that of Ms Dean and her relatives had been informed.
Following a post-mortem examination, the death is not being treated as suspicious.
A large-scale search for Ms Dean took place, involving Police Scotland's mountain rescue team, the coastguard and the local mountain rescue team.
Full-time female workers in Northern Ireland are defying the gender pay gap to earn more than their male counterparts, official figures have shown.
[NEXT_CONCEPT]
A body found in Argyll earlier this month has been confirmed as being that of a missing woman.