“My career never recovered and never will,” said Charlotte Brock, 39, a mother in Vienna, Va. When she had her first child eight years ago, she quit her job as a think tank analyst and moved in with her parents because she had no paid leave.

Now an analyst at NASA, she is expecting twins, and has pieced together sick leave followed by part-time work. Her husband doesn’t get paid parental leave either. “People don’t realize the recovery for women, even physically, is a lot longer than what’s advertised in our culture,” she said. “And just in terms of the experience of bonding, the closeness, and breast-feeding is so much easier if you can do it without having to pump.”

The share of American women who are working has stalled, researchers say, hurting families’ incomes and the country’s economic output, even as that share has continued to climb in other rich countries. As employment has improved since the last recession, men have benefited more than women. Economists have pinpointed the lack of family-friendly policies as a big reason. In Canada, by comparison, some parents can stretch out their paid leave over 18 months, and in Britain, many parents can take one year. Both nations also provide subsidized child care.

“Because we refuse to acknowledge that people have families and care issues, we’re falling behind our economic competitors,” said Heather Boushey, the executive director of the Washington Center for Equitable Growth, who advised Hillary Clinton on economic issues during her 2016 presidential campaign.

If policies like paid parental leave and subsidized child care enabled more mothers to work, the United States could add five million prime-age workers to its labor force, according to a new economic letter from the Federal Reserve Bank of San Francisco. Spending on child care makes the biggest difference in female employment, earnings and fertility, found a recent paper.

The California policy would be the nation’s biggest test of the idea that longer leave, by encouraging parents not to quit their jobs and by delaying the need to pay for infant care, can help economic growth.