The head of the team that will separate Preslee and Kylee Wells, who are conjoined at the chest and abdomen, says they have separate but joined hearts, livers and rib cages, The Oklahoman reported Wednesday.

Pediatric surgeon Dr. David Tuggle says the infants need to get bigger and stronger before surgery can take place unless their condition worsens.

If they don't share any important blood vessels around their hearts, a separation "would be fairly straightforward," Tuggle told The Oklahoman.

The infants were born by Caesarean section Oct. 25 to a 20-year-old woman who is a member of the Cheyenne River Sioux. They are believed to be the first known American Indian conjoined twins.