In the second half of the 20th century, the employment rate for women grew fairly steadily, but growth has stalled since the late 1990s, according to a report from Congress's Joint Economic Committee (as reported by the New York Times).
Bureau of Labor Statistics data show that women were particularly hard hit and did not recover from their job losses in the 2001 recession, unlike previous recessions, and that "wives are no longer insulating families from economic hardship in times of higher unemployment and falling or stagnant real wages," the report's authors conclude.
If the prior recession's trend holds, women will suffer equally to men in the 2008 recession. Because women are disproportionately represented in state and local government services, their job losses are likely to grow in the latter part of the recession as state and local governments are forced to implement cut-backs in spending in areas [where] women are disproportionately employed, such as education and health care.
Why is this a problem? The report finds that only those families with a wife who works have experienced real increases in income over the past three decades.
The study also makes the case that women aren't leaving the workforce to become mothers:
Women's larger job losses in the 2001 recession may also be due to women's progress in entering a wide array of industries and occupations. Because of this, women may be more susceptible to the impact of the business cycle than they were when they were more highly concentrated in a smaller number of non-cyclical occupations, like teaching and nursing. There is no evidence, however, that mothers are increasingly "opting out" of employment, in favor of full-time motherhood. For this story to be true, the employment rate of non-mothers would have had to diverge sharply from that of mothers, which has not been the case.