How can we find out if our twins are identical?

Content supplied by NHS Choices

Identical (monozygotic) twins are conceived when a single egg, released from an ovary, splits into two embryos after being fertilised by one sperm. The division often occurs after the egg has implanted in the wall of the uterus, and as a result, identical twins usually share a placenta but have their own cord and amniotic sac.

How to tell if twins are identicalIdentical (monozygotic) twins are conceived when a single egg, released from an ovary, splits into two embryos after being fertilised by one sperm. The division often occurs after the egg has implanted in the wall of the uterus, and as a result, identical twins usually share a placenta but have their own cord and amniotic sac.

Identical twins are always of the same sex (either girl/girl or boy/boy). If your babies share a sac in utero with no dividing membrane (called monochorionic/monoamniotic), they are definitely identical. A diagnosis may be given from the number of sacs seen on ultrasound scans, or after the consultant has examined the placenta at the time of birth. However, neither of these methods are foolproof. Other markers used to determine identical twins are eye and hair colour; blood groups; shape of feet, hands and ears; and pattern of tooth eruption.

Zygosity determination is the name given to the test to find out whether your twins are identical or fraternal (dizygotic). You may wish to know for sure:

  • in order to assist with medical decisions for your twins in later life (for example, to establish any genetic risk of illness),
  • if they wished to participate in twin research studies, or
  • simply to answer the inevitable questions from friends, relatives or strangers.

The most popular and accurate way to find out is to have a DNA test done, which involves sending a small swab of cheek cells (by sweeping a cotton bud along the inside of the cheek) away to a laboratory. This is not routinely available on the NHS, but is offered by the Multiple Births Foundation in the UK and by a number of organisations via the internet. The tests cost around £80 to £90 and results should be available within one month.

Further information:

Source:

NHS Choices

Published Date 2010-12-15

Last Review Date 2009-01-15

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