• Question: What is the chance of becoming a mirror image twin? (I am one)

    Asked by to Paul, Gill, Emma on 4 Jan 2019. This question was also asked by .
    • Photo: Gill Harrison

      Gill Harrison answered on 4 Jan 2019: last edited 4 Jan 2019 7:36 pm

      I didn’t really know much about this, as I usually only see twins before birth.

      I have found an article that suggests that 25% of twins that come from the same egg (monozygotic), which then divides into two, could be mirror-image twins. It seems to be down to the timing of when the egg divides. If it divides at about 9 to 12 days it’s likely to be mirror-image twins. Only about 1/3rd (1 in 3) of all twins are monozygotic, from a single egg and the paper I read said that about 25% (1 in 4) of these pregnancies are thought to be mirror-image twins. So I have done a calculation:

      The multiple births site http://www.multiplebirths.org.uk/media.asp suggests that there were 10,786 twins in 2016 in England and Wales. By my calculations that would suggest that approx. 809 of these twins are mirror-image twins like you in that year.

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