Since women generally have custody of the children, they end up paying for most of their support, including childcare. Single mothers are not always able to work as much as they need to. They often give up some employment opportunities in order to care for their kids. Women earn less per hour than men. Nationally, women earn 72.3 cents for every dollar a man earns.
Women generally have lower paying jobs and fewer promotions.
With less working time and lower wages, in turn, there are lower retirement savings and Social Security for women.