Every twin parent has heard this question about a billion times: "Do twins run in your family?" The answer to that question depends on many things, but is primarily related to whether your twins are fraternal or identical.
The Genetics of Fraternal Twins
Fraternal twins results when two eggs are fertilized instead of just one. Unlike identical twins, these twins have no more DNA in common that regular siblings. It has been long known that women in a family that includes fraternal twins are more likely to have fraternal twins. Recent research has isolated two genes that may be responsible for fraternal twins running in families.
The first is near a gene called FSHB, which is involved in FSH (follicle-stimulating hormone) production. Levels of FSH change as eggs in the ovaries mature. When the levels stay too high for too long the ovaries will release multiple eggs. Having multiple eggs is required to have fraternal twins.
The second gene is called SMAD3. This gene has been shown to change how ovaries respond to FSH in mice. Assuming it does the same for humans, this could also contribute to multiple egg releases in a cycle.
These genes are passed to both female and male children, which may account for the myth of fraternal twins skipping a generation. A male child can carry the gene, but it won't affect his partner's egg production. Their female child could inherit the genes that increase the chances of fraternal twins from her father and then go on to have fraternal twins.
Genetics of Identical Twins
It has long been thought that identical twins are not hereditary. Identical twins occur when a single fertilized egg splits into two. It is not known why this occurs and was thought to be totally random. However, families with statistically unlikely numbers of identical twins is causing geneticists to question whether or not it may be hereditary. They are looking into the possibility that genes involved in sticking cells together may contribute to the creation of identical twins.
Geneticists that have examined family trees with higher than normal incidents of identical twins have determined that the gene causing identical twins is passed to both female and male children and that you only need one copy of the gene for the trait to be expressed.
This follows what I see with my own family tree. I have a set of identical twins. My male cousin has a set of identical twins. And my female cousin has a set of identical twin grandchildren.
Non-Genetic Causes of Twins
Just because you had twins, it doesn't necessarily mean they run in your family. Here are some possible causes other than genetics for conceiving twins.
It should come as no surprise that the most common cause of twinning today is fertility treatments. Fertility treatments increase your odds of both identical and fraternal twins.
Another factor is your age. If you are over 35, your chances of having fraternal twins increases.
There is some evidence that women with a higher fat diet have an increased chance of having fraternal twins.
If you conceive in the cycle after coming off the pill, your odds of having fraternal twins is increased.
Twins Questions Shirts
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I see a lot of confusion among expectant twin moms over what type of twins they are caring. I hoping this post will help to clarify that confusion.
MoMo Twins - Monochorionic Monoamnionic
MoMo twins are the rarest type of twins. They are also the highest risk type. These types of twins are always identical. I am very familiar with the risks associated with these types of twins because my twins were MoMo twins.
Because they share one amniotic sac, they are at risk of cord entanglement and compression. I went into the hospital at 28 weeks for consent fetal monitoring of the babies so we would know if either went into distress due to cord issues. I have a picture of my twins cords taken right after they were born. It was very scary to look at all the knots in their cords. We were extremely lucky that they were able to make it to 35 weeks.
MoMo twins are always delivered early and are always delivered via c-section. My doctors said they almost never let MoMo pregnancies go past 34 weeks and they rarely make it to a scheduled c-section due to cord issues.
Because the babies share a placenta (the chorionic sac is associated with the placenta, one chorionic sac = one placenta), another risk to these types of twins is TTTS = Twin to Twin Transfusion Syndrome. This happens when one twin gets more nutrition from the placenta than the other twin. This is normally diagnosed by the size of the amniotic sac, but since this type of twins share an amniotic sac, they diagnose it by comparing the size of the babies.
MoDi Twins - Monochorionic Diamniotic
MoDi twins are almost always identical. They are not as high risk at MoMo twins, but are high risk than DiDi twins. Like MoMo twins, MoDi twins are also at risk for TTTS. It is easier to diagnose MoDi twins because they each have their own amniotic sac. Doctors are able to diagnose TTTS by measuring the fluid in each baby's amniotic sac.
Because they share a placenta, MoDi twins are usually delivered by week 36 due to concerns over placenta deterioration.
DiDi Twins - Dichorionic Diamnionic
DiDi twins are the most common twin type. DiDi twins can be either identical or fraternal. DiDi twin pregnancies are the lowest risk type of twin pregnancies. They are higher risk than a singleton pregnancy, but as far as twin pregnancies go, you hit the jackpot risk wise! The biggest risk for this type of twin pregnancy is preterm labor. However, unlike MoMo and MoDi pregnancies, DiDi pregnancies can be allowed to go full term. But most doctors will deliver you by 38 weeks.
Why does twin type matter?
It is very important that your doctor knows which type of twins you are expecting. Twin type is determined during your first ultrasound and verified during each subsequent ultrasound.
How often you are monitored, when you are delivered, and what risks you twins face are all dependent on the type of twins you are carrying. If you are carrying MoMo or MoDi twins you will be referred to a high risk OB and monitored much more frequently than DiDi pregnancies.
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Happy 4th of July!
We hope you all have a great day celebrating. Holidays with little ones can be challenging, especially if you have twins. Try and arrange your festivities around nap time. Bring along your play yard to give them a safe place to play while you enjoy your picnic. If you take them to a fireworks display, get ear plugs, hearing protective earmuffs, or hearing protective infant hats. Kids' eardrums can be damaged by the loud noises. Don't forget to document the day with lots of pictures.
We are thrilled to be able to offer custom ornaments featuring photos of your twins this year! Customize them with your twins name and year of their First Christmas. Upload your picture and create a special keepsake that will be treasured forever by you and your twins.
Tip for getting your picture just the way you want it: Once you have uploaded your picture and changed the text to reflect the info for your twins, click on “customize it” then on “design”. From there you can click on your picture to drag it to just the right place and drag the edges to make it bigger or smaller to get just the picture just perfect for your custom ornament.
We offer a variety of Valetine’s Day themed items for all members of your family! We have a special design just your twins’ first Valentine’s Day. We also offer “We heart heart” designs for mommy, daddy, grandma and grandpa that will be so cute for your twins on Valentine’s Day. Don’t forget to get yourself an “I heart heart my twins or triplets” shirt too!
You can even add your own text to our graphics to create a custom design all your own! You can also add names or other text to any one of our designs. Just click on “Customize It” from the product page and you can add your own take to our graphics.