It is rather important to note that the
wage gap does occur though because of events often 'caused' by marriage - children.
Quite often women's careers are put on hold, or go a less demanding (and less compensation) direction after childbirth. Women are often the ones agreed to in the marriage to stay at home with the children, whether for a few months or a few years. And after they do return to the workforce it is often agreed by the couple that her career be 'less demanding'. Someone needs to be available when children get sick, when they need to be transported to events, to be always home in the evening. Often women after childbirth tailor their jobs to be more flexible with regards to the demands of children - and those jobs often pay less.
If they do go back to their 'pre-childbirth' careers - their career has been 'put on hold' for the amount of time they were off - therefore will lag behind their male counterparts with regards to seniority and compensation. And there is also the thought in corporate America that mothers will be less available for the demands of highly compensated, and often highly demanding, with regards to hours worked, positions. They are often 'mommy tracked' and see fewer opportunities with regards to advancement. The study linked above shows that working moms average 5% less compensation per child when compared to men in similar jobs.
Also, it was interesting to note that when compared to a single woman, a mom applying for the same job was offered $11,000 less for the same position (if it was even offered to them, mothers, with the same experience and education were often 'circular filed' and not even considered for the position), reflecting the employer's concerns regarding the demands of motherhood and the interference it could cause in the workplace. But, fathers were likely to be compensated more than their single male counterparts, with employers regarding fatherhood as a stabilizing factor, and reward that attribute accordingly.
Yes,
women's pay has started to make big inroads into compensation inequality, and the numbers are starting to level out between the sexes, but
mothers' pay has not.