Moms with stable employment may be mentally and physically healthier at age 40 than mothers who's employment is more precarious.
The research from Penn State was presented at a meeting of the American Sociological Association recently.
Researchers say mothers who want to work but are continuously unemployed tend to be the least healthy.
They blame stress of finding and losing jobs.
The study included an analysis of data on more than 2500 women over the past 30 years.