All About Identical Twins
Identical twins happen in around 4 in 1000 pregnancies. These rare and special babies have fascinated people for centuries, and while we don't know everything, we do know that they have their own unique challenges and complications that parents face. This page hopefully will help explain a few of the many facts about twins.
Not All Twins Are The Same
There are different types of twins, and it's really important to know what type you're having! It all comes down to the number of placentas, and the risks associated with this.
Dichorionic Twins
Dichorionic twins have their own placenta, and own amniotic sacs. While still high risk, they are the most common type of twins, and the lowest risk. Pre-eclampsia, HELLP Syndrome, and gestational diabetes, along with fetal growth restriction are common concerns in these pregnancies. These twins still need close monitoring and checks from a maternal-fetal medicine (perinatologist) regularly.
These twins can be same gender, or opposite genders, and generally happen when 2 sperm fertilize 2 eggs at the same time, and implant.
They can also be identical twins (if the embryo splits between days 1-3).
If the twins are the same gender, zygosity testing should be considered if it is not established through routine checks in utero.
There are different types of twins, and it's really important to know what type you're having! It all comes down to the number of placentas, and the risks associated with this.
Dichorionic Twins
Dichorionic twins have their own placenta, and own amniotic sacs. While still high risk, they are the most common type of twins, and the lowest risk. Pre-eclampsia, HELLP Syndrome, and gestational diabetes, along with fetal growth restriction are common concerns in these pregnancies. These twins still need close monitoring and checks from a maternal-fetal medicine (perinatologist) regularly.
These twins can be same gender, or opposite genders, and generally happen when 2 sperm fertilize 2 eggs at the same time, and implant.
They can also be identical twins (if the embryo splits between days 1-3).
If the twins are the same gender, zygosity testing should be considered if it is not established through routine checks in utero.
Monochorionic Twins (Identical Twins)
Monochorionic twins happen when one fertilized egg splits to create 2 embryos. These twins share the same genetic material, and are in the vast majority of cases the same gender - except in really rare situations (for example, chromosomal abnormalities like Turner Syndrome, or chimerism).
These twins share a placenta, and this is what puts them at risk of diseases like Twin-Twin Transfusion Syndrome (TTTS), Twin Anemia Polycythemia Sequence (TAPS), and Selective Fetal Growth Restriction (SFGR) . There is also an exceptionally rare complication called Twin Reverse Arterial Perfusion (TRAP) Sequence, where one baby will not develop proplerly, causing problems for its co-twin.
The risks lie within the shared circulation in the placenta. These babies have connecting blood vessels, and this means that they need specialist care. For this reason, these pregnancies are monitored very closely by a maternal-fetal medicine specialist (also known as a perinatologist). Each of these diseases does have its own associated risks and treatment options, which you can learn more about on their own dedicated pages.
Monochorionic twins happen when one fertilized egg splits to create 2 embryos. These twins share the same genetic material, and are in the vast majority of cases the same gender - except in really rare situations (for example, chromosomal abnormalities like Turner Syndrome, or chimerism).
These twins share a placenta, and this is what puts them at risk of diseases like Twin-Twin Transfusion Syndrome (TTTS), Twin Anemia Polycythemia Sequence (TAPS), and Selective Fetal Growth Restriction (SFGR) . There is also an exceptionally rare complication called Twin Reverse Arterial Perfusion (TRAP) Sequence, where one baby will not develop proplerly, causing problems for its co-twin.
The risks lie within the shared circulation in the placenta. These babies have connecting blood vessels, and this means that they need specialist care. For this reason, these pregnancies are monitored very closely by a maternal-fetal medicine specialist (also known as a perinatologist). Each of these diseases does have its own associated risks and treatment options, which you can learn more about on their own dedicated pages.
- Twin-Twin Transfusion Syndrome (TTTS)
- Twin Anemia Polycythemia Sequence (TAPS)
- Twin Reverse Arterial Perfusion (TRAP)
- Selective Fetal Growth Restriction (SFGR)
- Uncomplicated Monochorionic Twins
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How Can You Tell If It's Identical Twins?
Even in the earliest ultrasounds, a skilled ultrasound tech can tell the number of placentas. It's all to do with the way the membrane looks on ultrasound. A thick divide between the twins means they have 2 placentas, while a thin, wispy divide (or no divide) means they share a placenta. This is important to establish very early on in the pregnancy, so that the right plan of action can be taken. By 16 weeks, you should be referred to a maternal-fetal medicine specialist (perinatologist) for screening every 2 weeks. Great Support Groups! One of the hardest parts about this type of pregnancy is that you might be alone and not know anyone with twins. That's why we've compiled a list of our favorite support groups for monochorionic twin pregnancies, to make your life easier and help you connect with people who have experienced the same things. |
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What we love about these groups is they're specilized for twins sharing a placenta. Because there are different risks for the different types of twins, it's really important to find people who can connect you to good quality information. We know these groups are evidence based, and follow the latest updates in research.
