Health Desk- Feb 28, 2019: Doctors have documented what they say is only the world's second known case of "semi-identical" twins.
The boy and the girl, now four, from Brisbane, in Australia, are identical on their mother's side.
But they share only a proportion of their father's DNA - placing them, genetically, somewhere between fraternal and identical twins.
Experts say the phenomenon is extremely rare - embryos such as these often do not survive.
The discovery was made through a routine pregnancy scan, said, Prof Nicholas Fisk, who led the team that cared for the mother and twins at the Royal Brisbane and Women's Hospital in 2014.
It is the first time semi-identical twins have been identified during pregnancy.
The first-time mother was 28 at the time and had conceived naturally, doctors said.
Courtesy: BBC Health