Progress has been slow — but momentum is building.

This week, New York City became one of a handful of U.S. cities to move to grant six weeks of paid leave, following the lead of places like Pittsburgh, Kansas City, Missouri, and Austin, Texas. Other cities have adopted smaller measures, while several financial firms and tech companies have begun to offer generous leave packages that, in the case of Netflix, could last a year.

But many other municipalities haven't joined them, largely because of financial constraints. Washington state, for instance, approved a paid paternal leave program in 2007 but has been unable to fund it. And while the Department of Labor has started giving grants to cities studying how to implement paid parental leave, legislation introduced in the U.S. Senate to pay for federally mandated leave appears to have stalled.

"I am heartened because these things are all connected, and each city that does it sparks another to do so," Ellen Bravo, the director of Family Values @ Work, a nonprofit coalition pushing for paid parental leave, said Wednesday. "But it'll be slow; it won't be a stampede. There are real financial or political challenges in many places."

In his State of the Union address, Obama noted that the U.S. was "the only advanced country on Earth that doesn't guarantee paid sick leave or paid maternity leave to our workers."

"That forces too many parents to make (a) gut-wrenching choice," Obama said.

In New York, Mayor Bill de Blasio announced he'll sign an executive order early next year to give the fully paid leave to 20,000 non-union municipal workers. De Blasio said the leave will apply to new mothers and fathers as well as to workers who adopt a child or become a foster parent.

Sadye Campoamor, who is six months pregnant and works for the city's Department of Education, said the new policy would allow her to bond with her child and help her avoid taking three months of unpaid leave, which is all federal law currently provides.

"The thought of having no pay for three months was terrifying me," she said. "Between student loans and living expenses, I was honestly not sure how we would do it."

Previously, those workers didn't have paid paternal leave and were forced to use sick days and vacation days. Administration officials urged the city's much larger unionized workforce, numbering about 300,000 employees, to adopt the benefit through collective bargaining. (Some of New York's most powerful unions signaled immediate support for the measure.) To cover the $15 million cost, the non-union employees will give back two vacation days, and the city will rescind a small portion of a planned 2017 raise.

Other U.S. cities also bolstered their plans this year. Chicago now offers four weeks for vaginal births and six weeks for C-sections. Boston now offers six weeks, with the first two weeks at 100 percent pay, the next two at 75 percent and the final two at 50 percent. Other cities offer paid leave benefits that kick in only after some sick days are exhausted. (San Francisco has the most expansive program, offering 12 weeks after some sick days are used.)

Three states — California, New Jersey and Rhode Island — also have paid family leave policies in place, while 18 other states are considering similar measures. And lawmakers in Washington, D.C., have introduced a bill that could offer the most generous leave yet: 16 weeks, fully paid.

Some municipalities have chosen not to pursue the program, believing the costs would outweigh any benefits. But U.S. Sen. Kirsten Gillibrand, D-N.Y., said the recent run of cities adopting leave programs is proof there is appetite for federal legislation, which she is sponsoring.

"This new policy is another clear sign that cities across the country are realizing the value of family-friendly workplace policies," she said.