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At what point will I know if my twins are identical?It's only natural to want to know as early as possible if your twins are identical. You may need to know in order to help in making medical decisions for your twins in later life (for example, to establish any genetic risk of illness), or to assess your likelihood of having twins again. You may want to find out simply for your own interest, and to reinforce your determination to treat your twins as individuals. Later, the twins themselves will want to know.It's also important for you, your doctor and your midwife to know whether your twins are identical as early as possible, because this will have an impact on the type of prenatal care you'll have during the rest of your pregnancy. Some types of identical twins are at a greater risk of complications than others, and will be particularly closely monitored. How easy is it to establish whether twins are identical?The only way of knowing for certain that your twins are identical is if, on an ultrasound scan, the ultrasound tech can see that your babies share an inner sac (chorion) with no dividing membrane (called monochorionic/monoamniotic). This means they are definitely identical.As they carry the same genetic package, identical twins are genetically identical and so are always of the same sex (either girl/girl or boy/boy). If the ultrasound tech detects two sacs (dichorionic/diamnotic), your babies may or may not be identical. About one third of dichorionic/diamnotic identical twins are in separate sacs, too. (Read more about how ultrasound can tell if your twins are identical) Although sharing a placenta may be a sign that your twins are identical, the placenta itself isn't a guide, as the placentas of non-identical twins can fuse together. And in a few cases identical twins can have a placenta each – this happens when the fertilized egg (zygote) splits within three days of conception. You may discover that your twins are identical at the time of their birth, after your doctor has examined the placenta. Even this isn't foolproof, however. As your babies grow, there are other markers that can be used to determine if they're identical. These include blood groups, eye and hair colour, the shape of feet, hands and ears, and the pattern of tooth eruption. But if you want to know for sure whether your twins are identical, the most accurate way to find out is to have a DNA test done. The test, known as "zygosity determination", will establish whether your twins are identical (monozygotic) or fraternal (dizygotic). It involves sending a small swab of cheek cells (which is done by sweeping a cotton bud along the inside of the cheek) to a laboratory. In Canada, you can have this testing done by a multiple births specialist in the Department of Laboratory Medicine and Pathology at the University of Alberta Hospital for a reduced fee. At the time of publishing it cost $100 for infant blood or placenta testing; $190 for infant cheek swab testing. A fact sheet on zygosity determination is also available from Multiple Births Canada. You can also have the testing done at a private biotech lab in Canada. If you’re hoping for or carrying twins you’re probably very curious to know if they’re going to be identical or non-identical (fraternal)! Approximately 1.54% of all births in the UK are recorded as multiple births including twins, triplets and more, and you should find out if you’re carrying during your dating ultrasound scan. Before then here’s all you need to know about what your chances are of having twins and what type of twins. There are 3 types of twins (and these apply to triplets too):
The other two-thirds of identical twins are MCDA, and just 1 in 100 identical twins are MCMA. Twins and your dating ultrasound scanBetween 8 - 14 weeks of pregnancy you’ll have your dating ultrasound scan where your sonographer will have a first peek and identify if you’re expecting multiple babies. If you are, the next step will be to identify the chronicity of your pregnancy - whether or not your eggs are sharing the same placenta (monochorionic) or if they have their own separate placentas (dichorionic). If your eggs are sharing a placenta you’re expecting identical twins! If they have separate placentas it’s nearly certain that the will be fraternal (non-identical) twins, but it is still possible they might turn out to be identical as 30% of identical twins don’t share a placenta. Fraternal (non-identical) twinsThere are a number of factors we know increase the likelihood of giving birth to fraternal twins:
Identical twinsWhat exactly causes identical twins to form remains a mystery, however there are some facts we do know that effect having identical twins:
You can produce identical twins when a single egg is fertilised by a sperm to form a zygote, which then goes on to divide into two separate embryos in the womb. Identical twins are genetically extremely similar and as such will typically look very alike - identical even! How can doctors tell if twins are identical or fraternal?Sometimes health care professionals identify same-sex twins as fraternal or identical based on ultrasound findings or by examining the membranes at the time of delivery. The best way to determine if twins are identical or fraternal is by examining each child's DNA.
Can identical twins be in different sacs?In the mother's womb (uterus), most identical twins share the same placenta. (They get oxygen and nutrients from the mother and get rid of wastes through the placenta.) But they usually grow within separate amniotic sacs. In rare cases, identical twins share one amniotic sac.
Can you tell if babies are identical or fraternal in the womb?However, when a twin pregnancy is evaluated by ultrasound, it's impossible to tell directly whether the twins are identical or fraternal. That determination must be inferred by looking at two things — the sex of the fetuses and the number of placentas and sacs present.
Can you tell if twins are identical or fraternal before they're born?If you're expecting MCDA or MCMA twins, you should find out whether they are identical at your dating scan, between 10 weeks and 14 weeks of pregnancy (NHS 2019, NICE 2011). Before 14 weeks, it's easier to see on a scan whether your babies each have their own membranes (NICE 2011, RCOG 2016).
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How to identify identical twins in the womb
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