A recent global wage study from the International Labour Organization, an agency within the United Nations, found that women at the top of the wage scale in 38 countries surveyed in 2010 had the greatest disparity in pay compared with their male counterparts. In Europe, for example, the top 10% of female earners made nearly 700 euros ($868) less per month than the top 10% of men. The bottom 10% of female earners also made less than the bottom 10% of men, but the difference was only 100 euros ($124) per month.

The ILO says the actual, overall gender pay gap varies from a difference of around 4% to 36% in all of the countries surveyed, which include the United States. In the U.S., the gap between men and women in the top 10% of high-earners in their respective genders is about $3,500 per month, according to the ILO. That’s compared to a difference of roughly $500 for the bottom 10%.

The study also took into consideration such factors as education, work experience, seniority, location and the number of hours an employee works. ILO found that women had a better combination of those factors in almost half of the surveyed countries, though the gap in wages does not reflect that fact.

In many countries, motherhood is a major factor in the wage gap, the study found. In Mexico, for example, mothers earn 33% less than non-mothers, while the motherhood wage gap is at least 20% in countries such as Brazil, Peru and Uruguay. In Russia, mothers earn only 2% less than non-mothers.