Kylie Mantz, who ran a 5:26.2 mile at 38 weeks pregnant earlier this month, and her husband, American marathon record holder Conner Mantz, have announced the birth of their first child, a son named William.
The couple shared the news in a joint Instagram post from Provo, Utah, writing that William was born “earlier this week.” They did not give an exact date.
“Words really can’t express how much we love our little Will,” they wrote. “We sleepy haha, but we’re happy and healthy.”
The post shows William in the hospital bassinet wearing a sage-green onesie with a Nike swoosh across the chest, a nod to his father’s employer. Conner, who has run for Nike since 2021, holds both American road records: 2:04:43 in the marathon, set at the 2025 Chicago Marathon, and 59:17 in the half-marathon, set in Houston in January 2025.
Kara Goucher, Keira D’Amato, Meb Keflezighi and Emily Infeld were among those offering congratulations, and the most-liked reply asked, “So what’s his mile PR?”
William’s arrival closes a pregnancy bracketed by racing. Kylie, 24, won the Two Cities Marathon in Fresno, California, on Nov. 2 in 2:43:49, with Conner pacing her, and learned weeks later that she had raced while newly pregnant. The couple announced the pregnancy on Valentine’s Day. On July 8 she posted the mile, run on the BYU track in a bib numbered 38, one for each week. “We started this pregnancy with a marathon, we’re ending it with a mile,” she wrote.
Before the pregnancy, Kylie was open about chasing the 2:37:00 qualifying standard for the 2028 U.S. Olympic Marathon Trials. “I think if I can figure out fueling, the OTQ is pretty obtainable,” she wrote on Strava after Fresno.
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