Representative Brittany Pettersen, a second-term Colorado Democrat, was not planning to have a second child at the age of 43.

“As if our life wasn’t complicated enough!” she said with a laugh as she arranged herself on a couch in her office on Capitol Hill earlier this week, staring down at her pregnant belly just weeks from her due date. She blamed the “mistake” on the confusion of working in two time zones. “It can make things hard with consistent birth control,” she said. “It was not part of the plan.”

Congress has existed for 236 years, but somehow Ms. Pettersen is about to become only the 13th voting member to give birth while in office, and the first from her home state. As Ms. Pettersen tries to plan the next phase of her life, the reality is setting in that this job was not created with someone like her in mind.

There is no maternity leave for members of Congress. While they can take time away from the office without sacrificing their pay, they cannot vote if they are not present at the Capitol. So Ms. Pettersen has taken a lead role in a new push by a bipartisan group of younger lawmakers and new parents in Congress to change the rules to allow them to vote remotely while they take up to 12 weeks of parental leave.

“This job is not made for young women, for working families, and it’s definitely not made for regular people,” said Ms. Pettersen. “It’s historically been wealthy individuals who are not of childbearing age who do this work.”

Before boarding her plane on Thursday to return to Lakewood, Colo., where she planned to remain until after she gives birth, Ms. Pettersen introduced the “Proxy Voting for New Parents Resolution.” It would change House rules to allow new mothers and fathers in Congress to stay away from Washington immediately after the birth of a child and designate a colleague to cast votes on their behalf.

“I feel really torn,” Ms. Pettersen said, “because I’m going to choose to be home to make sure that my newborn is taken care of, but I feel that it’s unfair that I’m unable to have my constituents represented at that time.”

The resolution, she said, “is common sense. It’s about modernizing Congress.”

The idea has been percolating on Capitol Hill for some time, but has become all the more pressing for the new Congress, its proponents argue, because the House is now so closely divided, with Republicans holding the majority by just one vote.

Republicans savaged former Speaker Nancy Pelosi for breaking with centuries of history and House rules by instituting proxy voting during the coronavirus pandemic. Former Representative Kevin McCarthy, as the minority leader, filed a lawsuit arguing that allowing a member of Congress to deputize a colleague to cast a vote on their behalf when they were not present was unconstitutional.

House Republicans also argued that allowing proxy voting would have a negative effect on member “collegiality.” Ms. Luna’s resolution never came to the floor for a vote.

Now, the bipartisan group is trying again. Ms. Pettersen’s resolution was one of the first introduced in the opening days of the 119th Congress. It is slightly broader than Ms. Luna’s original proposal, written to include proxy voting for new fathers.

“I’m not in favor of proxy voting; I think it should be very rare,” said Representative Mike Lawler, a New York Republican who welcomed his second child eight days before the election. “But I don’t think any member should be precluded from doing the job they were elected to do simply because they become a parent.”

Mr. Lawler, a leader of the new effort whose baby is 2 months old, cannot afford to be away from the Capitol while his party holds a one-seat majority.

“I understand the impact when you are given a choice between being home or coming and doing your job,” he said. “It’s not a great choice.”

Mr. Lawler dismissed concerns from House leaders about creating a bad precedent, saying the existing protocols no longer fit the Congress of the modern era.

“You have younger people getting elected to public office at a much higher rate than when these rules were established,” he said. “If we talk about being pro-family, you have to at least recognize that giving birth to a child or becoming a parent should not be an impediment to doing your job.”

Ms. Pettersen said she had considered having her baby in Washington so she could continue voting, but ultimately decided against it.

“It’s unfair to my family and unfair to my newborn if we’re not at home where all of our support and my doctor and support system is,” she said.

Ms. Pettersen is still relatively new to Washington and to motherhood — her son is still in prekindergarten — but the disconnect between her situation and the job of an elected official has been painfully obvious to her ever since she was pregnant with her first child and serving in the Colorado legislature.

Back then, she was the first member of that body ever to go on maternity leave. The only way to get paid while on leave was to categorize her situation as a “chronic illness.”

When she returned, Ms. Petterson successfully pressed to change the law to ensure that future state lawmakers would be given up to 12 weeks of paid parental leave.

Even before she walked the halls of Congress as the rare pregnant member, Ms. Pettersen said she felt like an odd fit for the Capitol.

When she was 6 years old, her mother was prescribed opioids after hurting her back and became addicted to heroine and then fentanyl. She overdosed more than 20 times. Growing up, Ms. Pettersen said, nobody even kept track of whether or not she came home at night.

“I saw Phish shows when I was 12 years old in Kansas and other places,” she said. “Still got straight A’s, though.”

(Her mother recently celebrated her 70th birthday and seven years in recovery.)

Because her parents were behind on taxes, she didn’t qualify for student loans, so Ms. Pettersen paid her way through school in cash, waiting tables, cleaning houses and working various odd jobs. She was the first person in her family to graduate from high school or college.

Beating the odds has made Ms. Pettersen even more determined to try to change her current workplace to make it feasible for more people like her.

“Being pregnant and being a member of Congress, people ask, ‘How are you doing this with your family?’ — all these questions I know my male colleagues don’t get,” she said. “It’s such a double standard.”