Correction: An earlier version of this article stated that Isabelle Marsh’s son is 2 and that her husband took two weeks of paid leave. Marsh’s son is 3 and her husband took one week of paid leave. The article has been corrected.

Every two years, like clockwork, federal lawmakers have tried to pass legislation mandating paid family leave. Sen. Kirsten Gillibrand (D-N.Y.) and Rep. Rosa L. DeLauro (D-Conn.) introduced their family leave bill in 2013 — and again in 2015, 2017 and 2019.

In 2021, the United States remains the only industrialized country in the world where parents are not guaranteed paid leave.

President Biden introduced legislation on Wednesday that could provide new parents with the kind of financial support received in other high-income countries. The $1.8 trillion “American Families Plan,” the second installment of Biden’s landmark infrastructure bill, calls for 12 weeks of paid leave for new parents by the program’s 10th year, with the amount of leave increasing over time. The plan offers a wide range of benefits for parents and families, including $225 billion to support national paid family and medical leave, along with $225 billion for child care and $200 billion for universal preschool for all 3- and 4-year-olds.

Only nine states and the District of Columbia have enacted paid family leave policies, and, as of 2019, only 19 percent of employees could access paid leave through their employers. While the United States does mandate 12 weeks of unpaid leave under the Family and Medical Leave Act, the policy excludes anyone working for an employer with fewer than 50 employees, as well as anyone who has worked for their employer for less than 12 months.

Even if they do qualify for the FMLA, most Americans can’t afford to go without a salary. To maximize their days at home after they give birth, salaried employees try to minimize time off during their pregnancies, cobbling together as much vacation and sick leave as possible. Hourly and contract employees lack even those limited options: If they miss work to have a baby, they might be out of a job.

The pandemic has provided a “historic, once-in-a-generation opportunity to right the ship,” said C. Nicole Mason, president and chief executive at the Institute for Women’s Policy Research (IWPR). With kids home from work and school, female workforce participation levels have sunk to 57 percent, the lowest they’ve been in over three decades, forcing government leaders to approach parent-centered policies with fresh urgency. If the American Families Plan passes with a robust family leave package, it could signal a “shift in our posture,” Mason said. Going forward, she added, child care could be seen as a “common good,” rather than a responsibility that falls only on parents.

But these policies will work only if there is enough money behind them, Mason said — and the Biden administration has drastically underestimated the amount necessary for paid leave. It will take $460 billion over 10 years to ensure that every new parent can take 12 weeks of paid leave, according to IWPR estimates, more than double the amount allotted in Biden’s proposal. The promises remind Mason of the War on Poverty, sweeping anti-poverty legislation introduced by President Lyndon B. Johnson in 1964.

“There were really robust policy ideas, but the investment just wasn’t there,” she said. And without the investment, she added, the Biden administration won’t see the returns.

More money would significantly strengthen the paid leave portion of the American Families Plan, Mason said. But the policies could still fundamentally change how women experience their pregnancy and first weeks of parenthood.

When Isabelle Marsh gave birth to her now-3-year-old son, she’d accrued only three days of paid leave as a new employee. The sole breadwinner for her family, she took another seven, unpaid, before she returned to work. Marsh said her employer offered no paid family leave.

Going back into the office, Marsh said, she felt physically unstable, struggling to find her balance when she walked. Her vaginal area was swollen and bleeding. For weeks, she wore a large pad and disposable underwear from the hospital.

“Imagine trying to get dressed in the morning and feel good about yourself,” she said. “Your body looks totally different. I couldn’t fit into any of my nice clothing.”

After she started wearing baggier clothes, Marsh said, she was approached by a manager who offered to buy her a new wardrobe on behalf of the company. “That brought me down even more,” she said.

Marsh’s husband, who wasn’t working at the time, stayed home with their son, Marcus. Sitting at her desk, Marsh would think back to the few days she had at home, cuddled up in bed with Marcus on her chest, wishing she could see him for more than a few hours each day.

“This sounds so bad, but I didn’t feel like his mom at all,” she said. “I felt like a roommate.”

Studies show that paid parental leave can improve mental health for new parents: Mothers who take longer periods of paid leave are less likely to experience postpartum depression. Marsh struggled with her mental health in her early days back at the office, she said — something she felt like she had to overcome on her own. Her colleagues rarely asked how she was doing, she said. They just asked about the baby.

“There were times I just wanted to cry,” Marsh said. “But I never felt like I could go up to my boss and ask if I could just take a half-day off.”

Alexandria Bennett says she also gave birth without paid leave. Working at a school, she had her now 12-year-old son one week into summer vacation and did not miss a single day of work. In the last few days of the semester, she started experiencing contractions. The school nurse urged her to go home, Bennett said. Instead, she sat in the nurse’s office until the contractions subsided, and went back to work.

“I was like, ‘No, I’ve got bills to pay,’ ” said Bennett, whose husband wasn’t working at the time. “It didn’t matter what was happening to my body. It didn’t matter if I was tired. It didn’t matter if my stomach seized up in a contraction. I had to keep my job.”

If Biden’s plan goes into effect, both parents would have the opportunity to spend an equal amount of time at home. While some countries give families a lump sum of leave to divvy up however they choose, Biden’s plan attaches 12 weeks to each parent. This policy will probably reduce stigma around paternity leave, said Gayle Kaufman, professor of sociology at Davidson College and author of “Fixing Parental Leave.” In many Nordic countries, men take three months of paternity leave, she said, “because that’s what’s expected.” If men across the United States begin taking 12 weeks off when they have kids, she added, that will become the norm.

The American Families Plan is unlikely to pass both houses of Congress without a fight, Mason said. The American Jobs Plan, the first infrastructure package released in early April, focused on construction, manufacturing and transportation, initiatives that fall under a more traditional definition of infrastructure. While it’s still unclear whether the two packages will be considered together or separately, Mason worries that the American Jobs Plan will be pushed through first, leaving less money and political capital for child care and paid leave.

Biden’s plan feels like a “breakthrough,” Marsh said. In September, when Marsh had her second child, she was working at a different company. This time, she had eight weeks of paid parental leave. Her husband, who also had paid parental leave, took one week off.

In those first two months, Marsh said, she hardly thought about work. She wasn’t worried about the financial ramifications of her pregnancy, she said, because there was still money coming in. With that “peace of mind,” she could be fully present with her baby.

“It was just her and I,” Marsh said, “just as I had envisioned it.”