Today "CBS This Morning" begins a four-part series, "The World of Mothers," which looks at what it is like to be a mother across the globe:

Hannah Cardin, a Massachusetts emergency room nurse and mother of two, did her best to prepare before Finnley arrived four weeks early via emergency C-section. She took on extra shifts, and even cashed out part of her 401(k), at a penalty, to keep her family afloat during her 12 weeks of unpaid maternity leave.

Hannah Cardin with her newborn, Finnley. The Massachusetts emergency room nurse could not afford to take 12 weeks off from work after giving birth. CBS News

"Everything that has been taught to me – no matter what happens, you never touch your retirement account because that's your account for later on – it's something that I had to do," Cardin said.

Even that wasn't enough. Cardin's husband lost his job; her income tax refund was less than expected; and with just $500 to spare, she must now go back to work early, 10 weeks after giving birth to a premature baby.

Correspondent Alex Wagner asked, "You scrimped, you saved, you try and get everything lined up, and the best laid plans aren't working out. What's your feeling about that?"

"It's definitely a defeating sort of feeling, you know?" Cardin replied. "I definitely wanted to spend those extra two weeks recovering, being with my family, and getting things in order. I'm still recovering."

Across the country in California, and a world away, Markita Staples-Green is getting ready to welcome her second baby girl.

As with her one-and-a-half-year-old daughter, Emerald, Staples-Green will take 26 weeks of fully-paid leave offered by her employer, software firm Adobe.

Markita Staples-Green, who is expecting her second child, will get 26 weeks of fully-paid maternity leave offered by her employer. CBS News

"By the time I went back to work, I was ready," Staples-Green said. "I was prepared: I had some time off to think about, 'Here's some of my goals, and here's going to be my new normal as a working mom.'

"I feel completely grateful. But I really wish that this was the norm."

The United States is the only developed country without a national, paid parental leave program. Most industrialized countries offer at least 14 weeks of paid maternity leave. The only national parental leave policy in the U.S. is the 26-year-old Family and Medical Leave Act, which guarantees workers job security for up to 12 weeks of time off, but there's no promise of a paycheck.

Six states and Washington, D.C., offer some form of paid family leave, but the majority of American workers are at the mercy of their employers.

Politicians on both sides of the aisle are working to change that.

The Democratic-sponsored Family and Medical Insurance Leave Act would give workers 12 weeks of partially-paid leave, funded by a payroll tax.

Republican Senator Marco Rubio told CBS News he is not in favor of mandating paid leave, and is instead taking a different approach. "It's an option that people can use to sort of draw on their retirement savings from Social Security early. But it's certainly better than having to max out your credit cards, or going on public assistance and leaving work, which is what a lot people have to do."

"It sounds like you see this almost as a sort of emergency situation, and this as an emergency solution," Wagner said.

"Well, it's certainly an emergency situation for someone who finds themselves six, seven, eight, nine months pregnant and realizes, 'I'm gonna have to miss two, three, four paychecks,'" said Rubio. "There aren't many people in America that can afford to do that."

Economists say paid leave programs have important economic benefits, like keeping women in the workforce who then can earn higher wages down the line. And a majority of Americans do support the idea of paid leave. It's only when costs are considered – whether it's higher taxes or a decrease in future benefits to pay for the leave – that enthusiasm decreases.

"There's a belief that individuals are responsible for taking care of their finances and their family, and so there shouldn't be government intervention; that's one main factor," said Loyola University Chicago professor Megan Sholar, who examined the nation's lack of paid leave in her book, "Getting Paid While Taking Time." "There's also a lot of opposition from business interests who fear any type of government regulation."

In the meantime, Hannah Cardin is doing what she can to make sure her family thrives.

"Eventually you just kind of have to continue living with what you have," Cardin said. "So, if I completely harped on the fact that there's no mandated maternity leave, if I harped on the fact that the finances aren't necessarily where I want them to be, the fact that I'm going back to work two weeks early, I wouldn't get the things that I need to get done, done."

While there is still deep disagreement about the specifics when it comes to paid leave and how to pay for it, the fact that there are an historic number of women in Congress today, and a looming battle over the female vote in 2020, will likely result in greater attention to issues like this one – and maybe even some solutions.