Well, as it’s the TAMBA Twins, Triplets and More week this week, I thought I’d mark the occasion by talking about all things twinny over the next few days!
To kick us off, let’s get back to basics with a biology lesson! Until I found myself pregnant with my two little bundles of joy, I never realised how much I didn’t know about multiples and there is an awful lot of misunderstanding about the facts of twinning – even a lot of midwives don’t know the full story! So here is a potted guide for you!
There are two main types of twins: identical and non-identical (aka fraternal).
Non-identical twins occur when two eggs are released at the same time and they are fertilised by two sperm. Genetically, non-identical twins are no more similar than any siblings – it’s just chance that they grow at the same time! Generally, non-ID twins grow separately in the womb, each having their own placenta and their own amniotic sac. In medical speak, this is known by the not-so-catchy title of Dichorionic Diamniotic (DCDA for short!) Non-ID twins can either be same-sex or girl/boy.
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| Image courtesy of Wikipedia http://en.wikipedia.org/wiki/Twin#Fraternal_.28dizygotic.29_twins |
Identical twins happen when one fertilised egg, inexplicably splits in two leaving two embryos that share exactly the same DNA. Medicine still has no real explanation for why it happens, but I feel very lucky that it did lol! This split usually happens between 1 and 8 days after fertlisation, but can happen as late as 12 or 13 days after. In the latter case, the sad result is conjoined twins as it is too late for them to separate fully.
Usually, ID twins share a placenta, but are separated from each other by a membrane, meaning that they each have their own amniotic sac. This is known as Monochorionic Diamniotic (MCDA). Identical twins are always same-sex. Occasionally, if the fertilised egg splits early enough, they will each have their own placenta, just like non-IDs. It is only possible to know if these types of twins are ID by conducting a DNA test and I know many families who later discovered that their non-IDs were actually ID all along which would explain how similar they look!
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| Image courtesy of Wikipedia http://en.wikipedia.org/wiki/Twin#Fraternal_.28dizygotic.29_twins |
Much more rarely (less than 1% of all ID pregnancies), the twins will share not only a placenta, but an amniotic sac as well. This situation is very high risk due to the possibility of the babies’ umbilical cords tangling and cutting off blood flow and intensive monitoring and premature delivery are usually required. As we discovered, thankfully this type of twinning is very rare and often misdiagnosed if the membrane dividing the babies is very fine and difficult to see.
In the case of triplets, quadruplets and more, you can get any combination of the above types, although identical triplets, quads etc. get rarer the higher the number of babies. They are more often all non-ID or an ID pair with one or more non-ID siblings.
So there you have it! With a few extremely rare exceptions, those are the main facts about twinning and if you’ve got to the end without nodding off at the back of the class, you now probably know more than your average nurse! I hope you found it enlightening in any case! For any parents of multiples who already know all this(!) pop on over to Two for Tea Creations on Facebook where I am offering 25% off all custom orders placed before 9pm on Saturday 9 July!
Up next: multiple myth-busters!
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