In his account of the Visitation, St. Luke says, "When Elizabeth heard Mary's greeting, the infant [John] leaped in her womb" (Luke 1:41).
Luke earlier states that when the angel of the Lord appeared to Zechariah—while he was offering incense—and announced the coming birth of John, Zechariah proclaimed, "He will be filled with the holy Spirit even from his mother's womb" (Luke 1:15).
Some infer from these texts that John was cleansed from original sin in his mother's (Elizabeth's) womb and thus born without original sin.
One is free to believe this, but it is not a necessary conclusion or a matter of faith, something that must be held.
While some believe John was freed from original sin while still in his mother's womb, the Church proclaims as a matter of faith that Mary, the mother of Jesus, was conceived without original sin, that she was never from the first instant touched by original sin.