Breanna Stewart is ready to tell her secret.

She kept it for months: During the first half of the current W.N.B.A. season, as captain of the Seattle Storm; in Tokyo this month, as she led the United States to Olympic gold in women’s basketball.

Only a few close friends, which included a pair of teammates, knew of her and her wife’s private joy.

“We just wanted to share this with a very close circle,” she told me last week, referring to herself and her wife, Marta Xargay. “Just to have this special time in life to ourselves for a while.”

Many consider Stewart the greatest female basketball player of this era. Now they can also call her a mom.

Stewart and Xargay’s gestational surrogate carried an embryo that had been seeded in one of Stewart’s eggs. Four days after winning a gold medal and most valuable player honors at the Tokyo Games women’s basketball tournament, Stewart experienced a moment that she said could compare with nothing else: the birth of her first child. “It took my breath away,” she said. “The most important moment of my life.”

The no-fanfare birth of Ruby Mae Stewart Xargay is a story of love and family in the modern age — without limits. It shows how female sports stars are pushing past tradition and finding a level of power that extends to every aspect of their lives.

“This is about controlling my own destiny,” Stewart told me. “It’s about making decisions that fit me, fit my family and where we want to go, where we want to be, and not waiting.”

Though still rare, having children and returning to competition is not new for the best female athletes. In recent years, a small number of mothers, about 10 or so, have played in the W.N.B.A. each season.

But Stewart, 26, and in her prime, is helping chart a new course. Having missed the entire W.N.B.A. season in 2019 because of an Achilles’ rupture, using a surrogate afforded her the chance to keep her career going without another interruption.

She is now the most prominent player to become a mother since the Women’s National Basketball Players Association championed a trailblazing labor agreement that set a new template for how sports leagues should treat women. Formalized in 2020, that labor deal did not just increase leaguewide salaries. It also ensured full pay for maternity leave, boosted access to child care and provided significant financial support for child adoption, surrogacy and egg freezing so that players can have children when the time is right.

“I’ve always known I wanted to have a family, always wanted to be a younger mom,” Stewart said. “It will not be easy, but why can’t I be the best player, a mom and have a child in the way we have done?”

Stewart pulled this off in what for her is typical fashion — carefully and tactically.

In 2017, her second year as a pro, she revealed in an essay that she is a survivor of sexual abuse endured in her childhood, using the public disclosure to advocate on behalf of other survivors. As an emerging star in a predominantly Black sport, Stewart had not spoken out much on matters of race. But starting last summer, after listening to her peers and getting involved in protests in the Seattle area, she began speaking loudly for Black justice.

For a long time she was quiet, too, about her relationship with Xargay, a now-retired Spanish basketball player with whom she had fallen in love while the two played on a Russian Euroleague team in 2019. But in May, Stewart posted to social media a picture of their engagement. The couple married on July 6 in a small ceremony atop their downtown Seattle condominium, details Stewart had not made public until now.

Stewart and Xargay decided they wanted a child in the summer and fall of 2020, as they huddled together through a W.N.B.A. season played in a bubble in Bradenton, Fla.

When the season finished, they interviewed surrogates and searched for the right sperm donor. Using an egg frozen during Stewart’s 2019 rehab, the pregnancy took hold. Then there were months of Zoom check-ins with the surrogate and her Idaho doctors.

All the while, Stewart had to keep her focus on basketball, which proved particularly challenging in Tokyo. So long as the baby didn’t come early, birth would be induced just after the Games.

Stewart said she had to compartmentalize as never before. “When it was game time at the Olympics, I focused fully on the game,” she said. “When I was off the court, I could think of Marta and the baby.”

In keeping with her private nature, Stewart was quiet about Ruby to her fellow members of the U.S. national team. She told me that only her Storm teammates and close friends, Jewell Loyd and Sue Bird, knew what was going on behind the scenes. Bird is a founder of TOGETHXR, the media company for which Stewart filmed a documentary about her surrogacy journey.

“I went from one emotion to the next,” Stewart said. “From winning a gold medal to realizing, OK, I’m going home, and my daughter is going to be born in less than 24 hours.”

What a week she would experience. The gold medal mission accomplished, Stewart flew home with the team, arriving in Los Angeles on Aug. 8, a Sunday. From there she boarded a private plane to Boise, where Xargay and the surrogate waited. Last Monday afternoon, at the Birkeland Maternity Center, in Nampa, Idaho, Stewart and Xargay watched Ruby slip easily into the world.

The brown-haired girl’s wailing shrieks filled the room. She weighed 9 pounds 4 ounces. “I was in shock, seeing a baby being born in front of me,” said Stewart, who stands an angular, broad-shouldered 6 feet 4 inches. “I felt like crying. I also just felt the love that was in the air.”

Stewart cut the umbilical cord. Soon, she and Xargay held Ruby for the first time. They laid their baby on a bed. They placed the freshly won gold medal at Ruby’s side.

On Thursday, Stewart was back to basketball. She flew alone to Phoenix, where the Storm played the championship game of the W.N.B.A.’s inaugural Commissioner’s Cup, a midseason tournament featuring the teams with the best records from the league’s two conferences. Stewart scored 17 points, missing just two field-goal attempts, and the Storm defeated the Connecticut Sun, 79-57.

When the game was done, she pulled her team around her in the locker room.

“I just wanted you guys to know that Marta and I had a baby,” she remembered saying to a sea of stunned faces. “It was like, ‘Wait, neither one of you are pregnant, so how can that happen?’”

As she explained, her teammates showered her with hugs.

Stewart told me she would miss only two Storm games to bond with Ruby and to rest. When the Storm play the Liberty for the second time this week on Friday night, she will be there.

There is no slowing down in professional women’s basketball. The top players go from battling through W.N.B.A. seasons in America to months spent overseas, seeking to maximize their earnings while still in their prime.

It is a grinding treadmill Stewart has been on since she left UConn in 2016. She will not stop. Only now she will have baby Ruby along for the ride, and no more secrets.