Can Twins Have Different Blood Types? Simplified Answer

It may be difficult to foresee which characteristics twins will share and which ones will distinguish them from each other. Despite considering factors like fingerprints and blood type, there is still uncertainty about which traits will vary or remain the same among multiple siblings.

Add in the fact that twins can be fraternal or identical, and there are many other factors to assess.

Can twins have different blood types? The short answer is yes, twins can have different blood types. Fraternal twins are more likely to have different blood types than identical twins, but it’s not impossible for even identical twins to have different blood types. It all depends on genetics.

Just like all things related to genetics, there are many factors that determine what blood type your children will have and if it will be the same as or different from their twin.

How Blood Type Is Determined

Your blood type is determined by genetics. Each child takes genes from both of their parents that determine if they will be A, B, or O, and they also inherit negative or positive Rh factors to determine their specific blood type. 

However, it’s a complicated enough process that parents with two different blood types could have children with types that don’t match the parents exactly.

Common Blood Types

There are eight major blood types. The most common include:

  • O positive
  • A positive

Rare Blood Types

The less common blood types are:

  • O negative
  • A negative
  • B positive
  • B negative
  • AB positive
  • AB negative

Which Parent Determines the Blood Type of the Child?

Both parents determine the blood type of their children. The genetic mix will control what type of blood your child has, and your child could end up with a different type of blood than either parent.

Does Blood Type Matter?

Blood type does matter. You should know what your blood type is so you know what blood you can receive should you need any. It’s also a good idea to find out what your children’s blood types are at birth in case they ever need blood.

There’s also information that shows people with certain blood types are at greater risk of health issues than those with other blood types. However, you can’t change your blood type.

Having the information about what your risks could be can help you take preventative steps, but it’s not something to obsess or worry about daily. More than just blood type affects your chances of certain diseases.

Does Blood Type Matter in Pregnancy?

For most people, blood type doesn’t matter during pregnancy. However, Rh factor, a component of your blood type, can affect mom and baby.

If you and your baby’s Rh factors don’t match during pregnancy (for example: you are Rh negative and your baby is Rh positive), problems can arise.

Your body can develop antibodies to your baby if your blood mixes with his, and that means your body might attack the baby.

This can lead to anemia for your child or even go as far as causing death. Illness or organ damage can also occur in your child if the Rh factor differences aren’t addressed.

Fortunately, doctors will test Rh levels and can inject Rh immunoglobulin to help prevent problems while you’re pregnant. However, this has to be done with each pregnancy if your Rh factor doesn’t match your child’s.

Do Identical Twins Have the Same Blood Type?

In the vast majority of cases, identical twins have the same blood type. Since they come from one fertilized egg that splits, identical twins share the same DNA.

Though it can mutate and cause differences, it’s rare for these mutations to affect something as major as blood type.

When Identical Twins May Have Different Blood Types

Since nothing is impossible, there is a minuscule chance that identical twins could have different blood types.

If a gene mutation took place when the egg was splitting and copying its DNA, one twin might end up with a different blood type. However, this is exceptionally rare.

Do Fraternal Twins Have the Same Blood Type?

Fraternal twins do not always have the same blood type. It’s possible that they will, but the chances are just as likely as any sibling pair since fraternal twins come from two different eggs fertilized by two different sperm.

Can Fraternal Twins Have the Same Blood Type?

Fraternal twins can have the same blood type. The best way to find out is to have their blood tested so you know what type of blood each has.

Do Twins Share Blood in the Womb?

Twins can share blood in the womb if they share a placenta. Mo/mo and mo/di twins share one placenta in the womb, so close monitoring has to take place to make sure one twin isn’t getting more blood than the other.

Twin-to-twin transfusion syndrome (TTTS) occurs when each twin is put at risk because one is getting too much blood and one does not have enough.

How Do I Find Out My Children’s Blood Type?

You can ask your child’s doctor if you need to know their blood type. A blood test or saliva test can be used to determine the blood type of your child easily.

You can even use an at-home kit if your child is okay with you pricking their finger to draw a bit of blood.

Related Questions: 

Can Fraternal Twins Be the Same Gender?

Fraternal twins can be the same gender. Though fraternal twins are only as genetically similar as non-twin siblings, they can still be the same gender. Both eggs can be fertilized by sperm that designates them the same gender.

Can You Give Blood to Your Twin?

Giving blood to your twin is just like giving blood to anyone. You have to be compatible donors, and that will depend on what type of blood each twin has.

If they have the same blood type, twins can definitely give each other blood. If not, it will depend on what type each one has and if it’s safe based on the blood types.

Closing Thoughts

Whether or not your twins have the same blood type will depend on what happens in the womb.