Jockey Rosie Napravnik revealed she is pregnant and plans to retire after winning at the Breeders' Cup meeting.
The 26-year-old won Friday's $2m (£1.25m) Distaff race in the United States on favourite Untapable.
It was Napravnik's second career victory at the event, known as the thoroughbred world championships.
"I've been planning retirement since I found out I was pregnant. I'm about seven weeks. Couldn't think of a better way to go out," she said.
Napravnik will race for a final time on Saturday at the two-day Breeders' Cup meeting.
The event, held at Santa Anita in California, offers $26m (£16.25m) in prize money, split across 13 races.
The final race of the weekend is Saturday's $5m Breeders' Cup Classic.