Twins share many things but do they have the same blood type?
Our identical twin girls share the same blood type and have the same blood type as their mother.
However, that doesn’t mean all twins share the same blood type.
Yes, twins can have the same blood type. But the answer isn’t that simple.
The types of twins you have and the genetics of the parents all come into play when determining your twins’ blood type.
(RELATED: Love podcasts? Check out the entire Dad's Guide to Twins Podcast archive for additional twin tips and interviews with twin dads.)
Do twins always have the same blood type?
No, twins don’t always have the same blood type.
Your twins blood type is determined by genetics and their parent’s blood types.
Twins often have the same blood type but do not necessarily have to have the same blood type. It often depends on the types of twins.
Identical twins almost always have the same blood type. Fraternal twins can have the same or different blood types.
Do identical twins have the same blood type?
Identical twins share the same DNA which includes the genetic codes that determine blood type. Having the same DNA all but guarantees that they will have the same blood type.
So yes, in addition to the same hair color, eye color, and physical features, your identical twins will share the same blood type.
(RELATED: Your twins will need a lot of gear. Here's the complete twins baby registry checklist to get ready for your twins' arrival.
There is the rare case where there is a mutation in the DNA of one of the twins and that could lead to different blood types for identical twins. But I wouldn’t count on that happening with your twins as it is very uncommon.
What type of blood will they have? That depends on the parents and the genetic roll of the dice.
Do non identical (fraternal) twins have the same blood type?
Since blood type is determined by the genetic rules in each child’s DNA, fraternal twins won’t necessarily share the same blood type.
With non identical twins, the blood type of each child is determined independently of the other. It is like comparing blood types of two siblings because they don’t share the DNA like identical twins.
(NOTE: Still expecting? Get weekly updates on your twin pregnancy here.)
Fraternal twins could each have their own type from the list of 8 common blood types.
What blood types could my twins have?
According to the Red Cross, there are 8 common blood types (A+, A-, B+, B-, O+, O-, AB+, AB-).
The most common blood types are O positive and A positive.
AB negative is very rare but maybe not in your case as everything depends on your genetics.
How is the blood type determined in your children? It is passed genetically from the mother and father.
Which parent determines the twins’ blood types?
If you remember your biology class in high school, genetic attributes from the mother and father help create a matrix of possibilities for the child.
The twins’ blood type then becomes a genetic game of dominant and recession traits with a sprinkle of statistics. This determines the type of genetic traits that are passed down from parents to their children.
Depending on the blood type of each parent, there are numerous possible blood types the children can have.
Due to all these possible combinations, the twins won’t necessarily have the same blood types as the parents. Yes, you could have four different blood types between Mom, Dad, and each of the twins.
If you want to dive into all the possible blood type combinations, compatibilities, and some data, the Cleveland Clinic has some great information about common blood types.
Do Identical Twins Share Blood?
During the twin pregnancy, twins can share blood. This happens when identical twins share a placenta in the womb also known as monochorionic twins.
Because these twins share a placenta, they share the blood from the placenta that contains all their nutrients that they get from Mom.
Occasionally, this leads to a serious medical condition called Twin-to-Twin Transfusion syndrome where one twin donates blood and nutrients to their twin. This results in one twin getting too much blood and nutrients (and getting larger) and the other twin getting too little (and not growing enough). This results in complications for both twins.
Why is blood type important?
If you or your children ever need a blood transfusion, it is important to have matching or compatible blood types. Otherwise, your blood may have an immune response that basically attacks the foreign blood in the system.
Generally speaking, the donor’s blood type has to match (have the same letter) as the recipients blood type. Any one with type O blood is a universal donor.
Does Blood Type Matter During Pregnancy?
During the twin pregnancy (or any pregnancy for that matter), there can be complications if the mother’s blood doesn’t match that of the baby or babies.
According to the University of Rochester Medical Center, Rh Disease happens when the Rh factor (that’s the positive or negative sign with the blood type) is a mismatch between mother and baby. It can also happen when blood types don’t match.
Just like if you got a transfusion of blood that didn’t match your blood type, Rh disease can cause antibodies in mother’s blood to fight the blood cells from the twins.
Mother’s and twins’ blood can mix during prenatal testing, other pregnancy complications, and at birth.
Talk to your doctor if you have questions about matching blood types.
How Will My Twins Know Their Blood Type?
Prenatal testing can help determine your twins’ blood types. Talk to your doctor if you’re interested in those details during the twin pregnancy.
After birth, blood tests are very common of newborns and your medical staff can let you know your twins’ blood type.
Once your twins are older, they may decide to donate blood or plasma. The Red Cross or donation center can test the blood type and let them know what type of blood they have.
Twins’ Blood Type and Growing Up Together
Because your twins are at least siblings, there is a great chance that they could share the same blood type or at least have compatible blood types.
This might come in handy later in life if they need a blood transfusion or other serious assistance from a family member. However, whenever health is involved, make sure you consult your doctor who best knows your twins’ medical history and blood types.