Because of a lack of widely available and affordable childcare and preschool programs -- as well as the lack of paid parental leave -- many women fall out of the US labor market when they become mothers.
"The US has the most inhospitable family policy of any country in the developed world," said Caitlyn Collins, a sociologist who has studied family leave policies in the US, Germany, Sweden and Italy.
Senator Elizabeth Warren, a Democrat from Massachusetts, raised the subject last month with the incoming US central bank chief, Federal Reserve Governor Jerome Powell -- asking him how policymakers could get women with caregiving duties back to work.
The Fed in fact has studied the issue, but has no authority to implement policy changes.
Paid (Other OTC: PAYD - news) maternity leave is a key factor. Though widely available in Europe and particularly generous in the Nordic countries, it is scarce in the United States. Federal legislation adopted in 1993 provides 12 weeks of unpaid leave to American workers, but does not apply to companies with fewer than 50 employees.
Private preschool and daycare is costly, with tuition sometimes running more than $30,000 a year. And even some women who can afford such steep bills sometimes throw in the towel and simply stay home.
- 'I loved my job' -
"Employers have become very demanding. They expect employees to work 60 hours a week," sociologist Pamela Stone told AFP. "They have to be reachable around the clock."
These working conditions are simply incompatible with family life, said Stone, author of "Opting Out," a study of women who left the career track to care for their children.
"It has nothing to do with motherhood ideology," she said. "They quit their jobs, but because the conditions of work are so demanding."
Tess Finnegan, a 44-year-old mother of three children aged 11, nine and six, learned the hard way. She (Munich: SOQ.MU - news) left her position as a federal trial attorney months after the birth of her first child.
"Before having children, I used to work 50-60 hours per week, traveling across the country," she said. "When I had my first child, I was lucky because I had some months off and then I went back to work part-time."
Soon, however, she was asked to return to her position full-time, with little chance to find daycare. So she left.
"It was a very difficult decision to leave my job. I loved my job," Finnegan said. She started a floral design business in 2014.
- Economic impact -
Economists say under-employing women or seeing them leave the workforce altogether represents a steep cost to the economy.
"If women entered and stayed in the workforce at a pace in line with, say, Norway, the US economy would be $1.6 trillion larger than it is today," according to research by S&P Global Ratings.
IMF Managing Director Christine Lagarde says gender parity in the workforce would add five percent to GDP. "Empowering women is an economic no-brainer," she said in a recent speech.
The US unemployment rate stood at 4.1 percent in November, the lowest in nearly 17 years as third-quarter GDP growth hit 3.3 percent.
The unemployment rate for women age 25-54, prime working years, stands at 3.6 percent, but that figure does not factor in women who have stopped working altogether.
Where they show up -- or rather, do not -- is in the labor force participation rate.
Those figures reveal that in 1990, American women's share of the workforce between the ages of 25-54 was among the highest in the world.
But it hit a plateau in 2000 and since then has gradually fallen back close to the 1990 level. It now stands 13 points behind that of men, at 75 percent against 88.5 percent.
In 2016, the United States was 20th in the OECD ranking of economies by women's participation in the prime-age labor force, according to S&P.