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August 27 is International Lottery Day, and when you find out you're expecting a baby and then—SURPRISE!—you find out it's actually twins, you may feel like you've won the lottery!
I mean, what are the chances of having twins?!
In Canada, approximately 1 in 31 births results in twins or higher-order multiples. In the United States, this statistic is almost the same, with about 32.1 out of every 1,000 births resulting in twins.
Triplets or higher-order multiples occur in about 78.9 out of every 100,000 live births.
There are factors that can contribute to increased chances of conceiving multiple babies, like:
- Genetics Having the hyperovulation gene, where your body releases two eggs—or more—during ovulation.
- Getting pregnant at an older age Where "old" is considered in your mid-30s or higher…I know, the term "geriatric pregnancy" is shocking the first time you hear it.
- Having a higher body mass index (BMI) You may be more likely to conceive multiple babies if your BMI is 30 or higher.
- Undergoing fertility treatments In-vitro fertilization or intrauterine insemination can result in multiple births from a single pregnancy.
Twinning it…but what kind of twinning?
Chances are good that you've heard of fraternal and identical twins. The type of identical twins you may carry depends on when the egg splits.
Division after one through four days results in Di/Di twins, division at four through eight days results in Mo/Di twins, and division at or through two weeks results in Mo/Mo twins. Division after two or more weeks results in conjoined twins.
There are also a handful of other types of twins you may not have heard about, and the chance of conceiving these different types of twins varies, too.
Different types of twins
1. Dichorionic Diamniotic (Di/Di)
Di/Di twins each have their own separate placenta and amniotic sac.
Genetically, if they are both the same sex, there is a 30 percent chance they will be identical and a 70 percent chance they will be fraternal.
If you're carrying Di/Di twins, you have a higher chance that your babies are siblings who happen to be in the uterus at the same time (wombmates, if you will) rather than them both having the exact same DNA.
There are doctors out there, including my own, who see two sacs and two placentas and automatically tell you your babies are fraternal, without knowing or even entertaining the idea that there's a slight chance they could actually be identical.
There are doctors out there, including my own, who see two sacs and two placentas (although, mine turned out to just be one huge placenta that tricked multiple doctors into thinking it was two separate ones) and automatically tell you your babies are fraternal, without knowing or even entertaining the idea that there's a slight chance they could actually be identical.
And if they are identical, one thing to keep in mind, when looking at your Di/Di twins and trying to decide if they're identical or not, is that just because they're identical twins, it doesn't mean they have identical DNA expression.
What does that mean? It means that your identical twins may not necessarily LOOK 100 percent the same. They can look quite alike but could still have slightly different appearances as a result of environmental factors that influence which genes are expressed and how.
2. Monochorionic Diamniotic (Mo/Di)
Mo/Di twins share one placenta but each have their own individual amniotic sac. They are identical.
Mo/Di twins are not the type of twins that run in families, and they occur in about three or four of every 1,000 pregnancies.
Carrying this type of twins is higher-risk than Di/Di because the placenta, which is usually meant to nourish just a single baby, is shared between both babies. Because of this shared blood supply, the placenta tends to "tire out" around 36 weeks' gestation.
Carrying this type of twins is higher-risk because the placenta, which is usually meant to nourish just a single baby, is shared between both babies.
Around this point, you run an even higher risk of running into danger with your unborn babies, so if your twins are Mo/Di, you'll go for screening more often than if you were carrying Di/Di twins (that is, unless you have other medical reasons for needing increased monitoring).
3. Monochorionic Monoamniotic (Mo/Mo)
Mo/Mo twins share one placenta and one sac and are considered incredibly high-risk.
If you're carrying Mo/Mo twins, you will go for even more frequent monitoring throughout your pregnancy to ensure your babies are healthy and measuring as they should be.
Mo/Mo twins are one of the rarest types of twins. They make up less than one percent of all births in the United States...
Mo/Mo twins are one of the rarest types of twins. They make up less than one percent of all births in the United States and about five percent of all monochorionic twin pregnancies.
4. Conjoined
Conjoined twins have bodies that are physically connected.
This type of twins occurs in about one in every 50,000 to 60,000 births. Interestingly, nearly 70 percent of conjoined twins are female.
About three-quarters of conjoined twins are connected in the chest and share organs.
About three-quarters of conjoined twins are connected in the chest (at least partially) and share organs.
In cases where each baby has a separate set of organs, the chances of separation (and of survival) are higher, but if they share a heart, they must remain conjoined.
5. Parasitic
A parasitic twin, also known as asymmetrical or unequal conjoined twins, is a type of conjoined twin where one twin is fully developed and the other fetus is undeveloped and does not survive the pregnancy.
This type of twins is very rare, happening in about 10 percent of all cases of conjoined twins; this equates to less than one in one-million births worldwide.
This type of twins is very rare, happening in about 10 percent of all cases of conjoined twins; this equates to less than one in one-million births worldwide.
With parasitic twins (also called vestigial or heteropagus twins), one fetus does not survive but remains attached to the other fetus (the dominant or autositic twin).
The dominant twin can end up being born with the limbs, organs, or tissues of the parasitic twin still attached and often requires medical treatment after being born.
6. Polar Body
Polar body twins are half-identical. They share about 75 percent of their genetic markers (less than identical twins do, but more than fraternal twins).
This type of twins occurs when one egg divides (which is a normal part of pregnancy), but is then fertilized by two sperm.
Polar body twins are half-identical... This type of twins occurs when one egg divides, but is then fertilized by two sperm.
This phenomenon gives them the same genes from their mother but different genes from their father.
Normally, a polar body doesn't survive the pregnancy, but sometimes, they can be strong enough to continue growing and develop into a viable fetus that completes a successful gestation alongside its twin.
7. Mirror
Mirror twins, while not officially medically recognized, are a subset of identical twins that seem to have reversed or asymmetrical (mirror-image, if you will) characteristics that reflect each other.
Mirror twins...seem to have reversed or asymmetrical characteristics that reflect each other.
This could be that one twin is right-handed, while the other is left-handed. Perhaps their hair parts on opposite sides of their head. Maybe their mouths feature reversed dental structures, or their bodies have organs on opposite sides (this is called situs inversus).
You won't see a medical professional officially determine a set of twins as Mirror Twins (there is no DNA-based zygosity test that can determine mirror image twins); being labeled a mirror twin is, essentially, decided by the twins or their parents based on observations of their features.
It's estimated that approximately one-quarter of all identical twins could fall into this subset.
But wait, there's more...
Beyond these types of twins, you can also have:
- Twins with different ages This is a result of superfetation, where a mother is pregnant and then, during her pregnancy, a second egg becomes fertilized and implants itself.
- Twins with different skin colors This can happen in three different ways, and you can read more about it, here).
- Twins with different fathers Yes, while rare, this is possible; the term for this occurrence is heteropaternal superfecundation.
Why is it important to know what kind of twins you have?
Twin pregnancies have a higher risk of going into preterm labor, and therefore, a higher rate of fetal and neonatal mortality, with the risk of fetal mortality being three to six times higher than a singleton pregnancy and neonatal mortality being seven times higher than a pregnancy with a single baby.
Once your twins are born, you may have other reasons for wanting to test whether they are monozygotic or dizygotic, like being able to assess your chance of conceiving dizygotic twins in the future, since that type of twins runs in families.
Or, perhaps, you're in a situation where one twin is in need of an organ or tissue transplant. In this case, an identical twin would often be an ideal donor, so having this information would be incredibly important.
Knowing whether your twins are identical or not can also help you assess critical factors, like illness or disorder risks, for your children.
Knowing whether your twins are identical or not can also help you assess critical factors, like illness or disorder risks, for your children.
Or, maybe people just keep telling you your twins look like carbon copies of ech other or always asking you if your twins are identical, and you just want to finally have a definitive answer to give people.
How do you find out what kind of twins you have?
If you want to find out what kind of twins you have, you can complete a twin zygosity DNA test.
Sometimes, you can ask your primary care provider or OB-GYN about this, as some offices offer a non-invasive prenatal test (NIPT) that can confirm this for you.
One such test is Natera's Panorama test, which screens pregnancies for zygosity, fetal sex of each baby, and identifies risks for more genetic conditions in twin pregnancies than any other non-invasive prenatal test.
With this type of test, sometimes, you run the risk of receiving inconclusive results, which can be common in twin pregnancies, as they may not be able to collect enough of both babies' DNA among the mother's DNA.
Unless you want to do the test again, you'd likely end up waiting until your 20-week anatomy scan to confirm the sex of your babies.
If your health care provider's office doesn't offer this sort of test, or if your babies are already born, but curiosity is getting the better of you (or your family and friends!), or if you have a nagging feeling your twins might actually be identical even though others are convinced they're fraternal, the following are the most popular twin zygosity DNA testing kits that can confirm things once and for all.
1. Genetrace DNA Twin Test
The Genetrace DNA Twin Test can confirm whether your twins are fraternal or identical. All lab fees and shipping costs are included, and you can receive results in one to two days.
2. Genovate Twin Zygosity DNA Test
The Genovate Twin Zygosity DNA Test gives you results in one or two days and can confirm if your twins are identical or fraternal.
3. My Forever DNA
The My Forever DNA test checks 24 genetic markers and gender identification marker amelogenin; the most DNA markers industry-wide. You can expect to receive results in one to three business days.
4. Affinity DNA
The Affinity DNA Test is a 99.99 percent accurate genetic swab test that can confirm twin zygosity. All fees are included and you can expect results in four business days.
5. AlphaBioLabs Twin DNA Testing Kit
With this test, the lab fee is paid separately from the test price, and you can expect to receive accurate results to confirm twin zygosity in three business days.
No more wondering…
There are many reasons why you may want to confirm whether your twins (or YOU, if you're a twin, like me!) are identical or fraternal.
Whatever your reason may be, clarifying your twins' zygosity can be done through a DNA test that looks at specific genetic markers, so you'll no longer have to wonder if you're truly identical or truly fraternal.
Either way, your twins are truly amazing.
There's no doubt about that.
Did you complete a twin zygosity DNA test to confirm whether your twins are fraternal or identical? What were the results? Were you surprised? Let us know in the Comments section below.
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