Washington: Twins from Brisbane, a boy and a girl, have been identified as only the second set of semi-identical, or sesquizygotic, twins in the world. They are the first to be identified by doctors during pregnancy.

The now four-year-old boy and girl are identical (monozygotic) on their mothers side sharing 100 per cent of their mothers DNA, but are like siblings on their fathers side, sharing only 78% of their fathers DNA.

This is the first case where semi-identical twins were identified on genetic testing while in the womb. It has been reported in The New England Journal of Medicine (NEJM) by Professor Nicholas Fisk and Dr Michael Gabbett. Sesquizygotic multiple pregnancy is an intermediate between monozygotic (identical) and dizygotic (fraternal) twinning… (NEJM; ET Health, February 28, 2019)