health
February 9, 2026
The Twins That Are Neither Identical nor Fraternal
They shared a placenta, but on the ultrasound, one looked like a boy, and the other a girl.
TL;DR
- Sesquizygotic twins are a rare type of twin that is neither identical nor fraternal.
- They likely result from an egg fertilized by two sperm (one X, one Y) and subsequent complex cell sorting.
- The twins are chimeras, possessing a mix of XX and XY cells in varying proportions.
- This is the second documented case of sesquizygotic twins, highlighting their extreme rarity.
- One twin experienced an arm amputation due to a blood clot and surgery for an ovarian abnormality related to chimerism.
Continue reading the original article