It’s been a big week for women in the workplace. According to a  Pew Research Center report (PDF) released on Wednesday, mothers now represent 40 percent of all breadwinners in U.S. households with kids, a huge gain from the 11 percent of 1960. Among today’s female breadwinners, 37 percent earn more than their partners in two-income households. The rest are single mothers. “The total family income is higher when the mother, not the father, is the primary breadwinner,” the Pew study noted.

But these mothers often have a smaller lead in income over their partners, compared to men who are primary earners. In other words, there’s still a persistent pay gap. Consider a  more sobering survey released on Thursday by  Citi ( C ) and  LinkedIn ( LNKD ) revealing that when a household has two incomes, the higher-earning wife will earn an average of $35,000 more than her spouse. When the husband earns more than his wife, however, his salary is larger by $49,000.

The driving force behind this discrepancy is male dominance of such occupations as managers and software developers, which pay more than traditionally female-oriented occupations, according to  data from the Institute for Women’s Policy Research (PDF). Linda Descano, president of Citibank’s  Women & Co. financial website, also cites the “lack of control that women feel over the factors affecting their financial futures and career advancement.” Seeking more money, for instance, can be difficult for women: Only one in four respondents in the Citi/LinkedIn survey reported asking for a raise in the last year—which is a particular shame because most of those who did ask said they received a salary bump. In addition to smaller salaries, women often feel they lack the opportunity to move up; fewer than 40 percent believe their current employers will promote them.

Work-life balance issues also pop out of the Citi/LinkedIn study, based on surveys of 954 working women. Nearly half of female breadwinners told the researchers that work is a source of tension at home, with many citing the pressures of being the primary earner and feeling that their partners aren’t doing enough around the house. ( Bloomberg Businessweek also looks at  how fathers address work-life balance .) “When we asked members of Citi’s Connect: Professional Women’s Network about their biggest obstacles to career success, self-doubt was the central theme of many of the comments,” says Descano. “Break down the roadblocks you may be creating for yourself first, then tackle the rest.”