Second ever case of semi-identical twins documented in Australia

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, the BBC reports.

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.

Prof Nicholas Fisk, who led the team that cared for the mother and twins at the Royal Brisbane and Women's Hospital in 2014, said the discovery was made through a routine pregnancy scan.

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.

The case is being reported on in The New England Journal of Medicine.

"The mother's ultrasound at six weeks showed a single placenta and positioning of amniotic sacs that indicated she was expecting identical twins," Prof Fisk said.

"However, an ultrasound at 14 weeks showed the twins were male and female, which is not possible for identical twins."

 

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