Fraternal twins are like a pair of siblings who happen to grow together in their mom’s belly at the same time. But here’s the twist: instead of one egg splitting into two, two separate eggs are fertilized by two different sperms. This means they’re like two separate pregnancies happening together!

Fraternal Twins: Varieties, Genetics, and Parenting

Now, identical twins are like a copy-paste situation. One egg gets fertilized, and then it splits into two, making two babies that share the same DNA. That’s why they often look so much alike.

But fraternal twins are more like regular siblings who just happen to be born at the same time. They can look alike or not so much, just like any other siblings. Their personalities and health stuff can also be similar or different, depending on their genes and the world around them.

So, in this article, we’ll talk about how fraternal twins happen, how they’re different from identical twins, what goes on while they’re growing in the belly, and if there are any health things to watch out for.

Facts about Fraternal Twin

When it comes to making fraternal twins, it’s like a special event in the body called “hyperovulation.” Normally, a woman’s ovaries release just one egg during her monthly cycle. But sometimes, they release two or even more eggs, which raises the chances of having twins.

Scientists found that women who naturally have fraternal twins tend to have higher levels of a hormone called follicle stimulating hormone (FSH) in their blood. This hormone helps eggs grow before they’re released. So, when there’s more FSH around, there’s a better chance of releasing more than one egg during ovulation. If one or more eggs meet sperm at the right time, boom—twin pregnancy!

Sometimes, twin pregnancies happen because of fertility treatments like IVF, where eggs are fertilized outside the body and then put back into the womb. These treatments have become more common over the years, so we’re seeing more twins born this way.

Now, let’s talk genes. Fraternal twins come from separate eggs, so they’re like regular siblings who just happen to be born together. They only share half of their genetic material, just like any other siblings born at different times.

Read More : Fraternal twins and Identical twins

Are Twins Hereditary?

Oh, got it! Imagine your body has a special way of deciding if it wants to have twins or not. Sometimes, it’s like a family secret—it runs in families. So, if your mom or sister had twins, it’s like a little hint that maybe you could have twins too!

Now, scientists have been snooping around in our genes to see if they can find out more. They discovered two genes called FSHB and SMAD3 that seem to be important. These genes have different versions, like different flavors of ice cream. Some versions make it more likely for a person to have twins. These genes control how much of a hormone called FSH is in your body. FSH is like a superhero hormone that helps eggs grow in the ovaries. So, if your genes make a lot of FSH, it could mean more eggs are released during ovulation, increasing the chance of having twins. And guess what? These gene versions can be passed down in families, so if your family has them, you might have them too!

 Contributing Factors to Having Fraternal Twins

  1. Fertility Drugs: Medications like Clomid can boost a hormone called FSH, which helps release eggs from the ovaries. This can increase the chances of having twins.
  2. Age: As women get older, their bodies naturally make more FSH. This hormone helps eggs come out of the ovaries. If there are two good eggs and lots of FSH, both eggs might come out, leading to twins.
  3. Family History: If twins run in your family, especially on your mom’s side, your chances of having twins go up. This is because certain genes for releasing more eggs can be passed down.
  4. Height: Taller people tend to have more of a protein called IGF, which makes ovaries more sensitive to FSH. This also increases the chances of releasing more eggs and having twins.

 Identical vs. Fraternal Twins:

– Origin: Identical twins come from one egg and one sperm, while fraternal twins come from two eggs and two sperms.

– Genes: Identical twins share the exact same genetic material, while fraternal twins are like regular siblings who share about half of their genes.

– Appearance: Identical twins usually look very similar, but fraternal twins can look completely different, just like any other siblings.

– Sex: Identical twins are always the same sex, but fraternal twins can be the same or different sexes.

– Hereditary Conditions: Fraternal twins can have different hereditary conditions based on the genes they inherit, while identical twins share the same genetic risks.

So, while identical twins are like two peas in a pod, fraternal twins are more like two different peas from the same pod!

Different Ways Fraternal Twins Can Happen:

  1. Regular Way: Usually, fraternal twins happen when two eggs are released from the ovaries and get fertilized by sperm around the same time. This is the most common way.
  1. Superfetation: This is super rare! It’s when a second egg gets fertilized and sticks in the uterus weeks after the first egg is already growing into a baby. You can suspect this if the twins are different sizes.
  1. Heteropterans Superfecundation: Another rare one! It’s when a woman releases two eggs during one cycle and they both get fertilized by sperm from two different guys, in two different times of having sex.

Testing, Growth, and Birth –Identifying Fraternal Twins:


If an ultrasound shows two babies with separate placentas and sacs, it’s likely fraternal twins. Twins of different sexes are also fraternal, while twins of the same sex can be fraternal or identical.

DNA Testing:

The surest way to tell is by testing the babies’ DNA after birth. If they share about half their genes, they’re fraternal.

Growth Issues:

– Intrauterine Growth Restriction (IUGR): Sometimes, one or both twins don’t grow as much as they should in the womb, which can cause health problems for them after birth.


Preterm Delivery: Twins often arrive earlier than expected, which can lead to health issues because their bodies aren’t fully ready. They have a higher risk of health problems and early death.

– Delivery Method: Many twins are born by cesarean section (C-section) because it’s safer for them or their mom, or because they’re premature or in a breech position.

So, while having twins is exciting, it can also come with some challenges. It’s important for doctors to keep an eye on the babies’ growth and for parents to be prepared for the possibility of a C-section delivery.

Parenting Fraternal Twins

Treat Them Individually: Each twin is unique, so it’s important to recognize their differences in personality, talents, and feelings.

– Give Them Space: Let each twin have time apart to develop their own relationships and skills. Spend one-on-one time with each, and encourage separate activities and classes as they grow.

– Seek Support: Don’t hesitate to ask for help from your partner, family, friends, or pediatrician when you’re feeling overwhelmed.

Understanding Twins through Studies:

Genetics and Environment:

Twin studies help scientists understand how genes and upbringing influence traits and health conditions.

Examples: For instance, if one identical twin has schizophrenia, the other twin has a high chance of having it too, showing a strong genetic link. But if one fraternal twin has it, the other’s risk is lower, suggesting a smaller genetic influence.

Ongoing Research: Researchers are studying twins with various conditions like diabetes and arthritis to learn more about their causes and treatments.


– Fraternal twins come from two separate eggs fertilized by two separate sperms and share about 50% of their DNA.

– Factors like fertility drugs, genetics, and maternal age can increase the chances of having fraternal twins.

– Twin pregnancies have risks like growth issues and early delivery, but with good prenatal care, these risks can be minimized.

In short, while fraternal twins share a special bond, they’re also unique individuals just like any other siblings. Understanding their differences and seeking support can make parenting twins a rewarding journey.


Q. Are the blood types of dizygotic twins the same?

Dizygotic twins, also known as fraternal twins, may or may not have the same blood type. Since they only share some of their DNA, it’s possible for them to have either the same or different blood types. In contrast, monozygotic twins, or identical twins, usually have identical blood types because they share the same genetic makeup.

Q. What accounts for the physical distinctions among fraternal twins?

The primary factor is their genetic makeup. Fraternal twins only share approximately 50% of their DNA. For example, one twin might inherit blue eyes from one parent, while the other twin inherits brown eyes from the other parent.

In essence, genetically, fraternal twins are akin to siblings born at different times.

Q. How do doctors distinguish between identical and fraternal twins in the womb?

Typically, fraternal twins develop with two distinct placentas, whereas identical twins share a single one. This difference can be observed via ultrasound. Additionally, if twins are born as different sexes, it’s highly probable they are fraternal (though same-sex twins can still be fraternal or identical).

However, the surest method to determine if twins are identical or fraternal is through DNA testing after birth.

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