Fraternal Twins Explained: How They Form, Unique Traits and Facts

Fraternal Twins: How They Form, Unique Traits, and Facts

Seeing two babies who look alike yet not identical intrigues people. These babies are fraternal twins, also known as dizygotic twins.

Fraternal twins form from two separately fertilized eggs and are no more alike than ordinary siblings born at different times. But their development together in the womb makes fraternal twins unique in many ways.

Here’s a look at how fraternal twins form, what makes them special, and some fascinating facts about these twin siblings.

How Fraternal Twins Occur

For fraternal twins to form, two events need to happen:

1. Hyperovulation - The woman’s ovaries release two eggs in one menstrual cycle instead of the usual one egg.
2. Double fertilization - The two eggs become fertilized by two separate sperm cells.

Fraternal twins can be:

• Boy/girl twins - One egg is fertilized by a sperm with an X chromosome, the other by a sperm with a Y chromosome.
• Same sex twins - Both eggs are fertilized by either two "X" or two "Y" chromosome sperm.

What Increases the Chance of Having Fraternal Twins?

Several factors make having fraternal twins more likely:

• Ethnicity - African ancestry increases the odds of hyperovulation.
• Family history - Having a twin sibling or twins in your family raises chances.
• Age - The frequency of fraternal twins increases after age 30.
• Body type - Being tall or overweight boosts hyperovulation risk.
• Prior births - Having already carried a pregnancy to term increases likelihood.
• Fertility treatments - Drugs that stimulate ovulation often cause fraternal twins.

Differences Between Fraternal and Identical Twins

It's important to understand how fraternal twins differ from identical twins, which form from one fertilized egg splitting into two embryos.

Fraternal twins:

• Have separate amniotic sacs and placentas
• Are no more alike than normal siblings
• May be different genders
• Do not have matching features and traits
• Develop their own separate identities

Identical twins:

• Share an amniotic sac and placenta
• Have almost identical DNA
• Are always the same sex
• Have nearly identical looks and traits
• Often feel like two halves of one person

10 Fascinating Facts About Fraternal Twins

Fraternal twins capture people’s curiosity. Here are 10 interesting facts about them:

1. They Run in Families

If you have fraternal twins, there’s around a 1 in 60 chance your siblings will also have twins. The hyperovulation tendency gets passed down genetically.

2. There Can Be a Big Size Difference

Unlike identical twins which are nearly always the same size, fraternal twins can vary greatly in size at birth. One twin may be 5-6 pounds bigger due to getting more nutrition in utero.

3. They Have Separate Birthdays Technically

Since fraternal twins grow from two different eggs, they have different conception days. So their actual birthdays are 1-2 days apart even if delivered on the same calendar day.

4. Their Bond is Special

While not as intensely close as identical twins, most fraternals develop a tight lifelong bond from sharing the womb. They play and communicate with each other before birth.

5. Mixed Race Twins Occur

If a woman of mixed race parentage conceives fraternal twins with two different fathers, she can birth twins with distinct skin colors and features.

6. Extremely Rare Twin Types Exist

In rare cases, fraternal twins can be born a day, week or even months apart if they implant at different times. Others may have different dads in extremely rare heteropaternal superfecundation.

7. Some Share a Placenta After All

While most fraternal twins have separate placentas, about 1/3 will share a placenta but always have distinct amniotic sacs. This gives them some traits of identical twins.

8. Their Environments Aren’t Identical

One twin may get slightly more blood flow or be in a better position in the womb. This exposes them to different nutrition and growth factor levels.

9. Mirror Imaging Occurs

Fraternal twins can exhibit mirror imaging. This is when features like birthmarks or hair whorls develop on opposite sides of their body.

10. Conjoined Twins Are Always Fraternal

Conjoined twins start as fraternal twins from two separate eggs. But the split into fully separate embryos is incomplete leading to twins born physically connected.

Unique Development of Fraternal Twins

The way fraternal twins grow and interact in the womb leads to some special attributes after birth.

How Fraternal Twins Interact Pre-Birth

Fraternal twins exhibit some unique behaviors before birth like:

• Playing together - Touching each other, holding hands, sucking each other’s thumbs
• Physical aggression - Kicking, hitting, pushing against each other
• Sharing resources - Consuming from the same placenta and amniotic sac
• Stimulating development - Motion and activity accelerate lung and brain maturity

Advantages Fraternal Twins Experience

Being a twin offers some mental and physical advantages such as:

• Earlier achievement of developmental milestones
• More advanced language development as toddlers
• Enhanced social skills and emotional intelligence
• Built-in companionship and friendship
• Lower risk of developing neurologic disorders

Disadvantages Fraternal Twins May Face

There are also some potential disadvantages fraternal twins may encounter like:

• Low birth weight and prematurity
• Developmental delays if born significantly premature
• Increased risk of twin-to-twin transfusion syndrome
• Higher parental stress providing double the care
• Trouble establishing individual identity

Parenting Fraternal Twins

Raising fraternal twins comes with special challenges. Here are some tips for parenting them:

• Give each twin focused individual attention daily
• Separate them occasionally to reduce codependency
• Reward and discipline them as individuals
• Watch for signs of competition or rivalry
• Celebrate differences instead of comparing abilities
• Set up playdates for each twin with different friends
• Have open discussions about their relationship
• Avoid always dressing them alike

The Outlook for Fraternal Twins

Fraternal twins hold an intrigue all their own. Their shared intrauterine environment and lifelong twin bond make fraternal twins a special subset of siblings to observe in life.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.