Fraternal Twins

It is indeed a double blessing for a parent who has twins, but it is also double the trouble. Raising twins can seem tough at times, but there are also some amazing things about having twins. Fraternal twins are the most common type of twins, and they do not share the same genes. Here, you can find out more about the different kinds of twins, how they are interesting and some surprising fraternal twin facts.

What are Fraternal Twins?

Fraternal twins or non-identical twins are either of a pair of twins who, as a result of developing from separate fertilized ova, are genetically distinct and not necessarily of the same sex or more similar in appearance than other siblings.

Fraternal twins in the womb, therefore develop after some special adaptations during foetal development.

How are Identical and Fraternal Twins Different? 

You may be wondering now how they are different from identical twins? To start with identical twins are born due to fertilization of one singular egg with a sperm, whereas fraternal twins are born due to the fertilization of two sets of eggs.

Monozygotic twins (also known as identical twins) share 100% of the same gene whereas dizygotic twins (non-identical twins) share only 50% . This is similar to the genetic familiarity found between siblings born at different times.

It is common to have a fraternal twin set with one of each gender as opposed to the same gender. For example, in 100 births there will be at least 2 fraternal twins making them more common than identical twins.

How do Dizygotic Twins Fit?

Dizygotic twins are the scientific name given to fraternal twins. ‘Di’ means two and ‘zygotes’ means fertilized eggs.

The fraternal twins have two different amniotic sack in the womb. They also have a separate placenta. This is medically called as being dichorionic-diamniotic (Di means two). The two different sacks ensure equal chances of survival for the twins.

How are Fraternal Twins Formed?

In a fraternal twin pregnancy, the first step that occurs is two eggs or ova are fertilised by the same sperm and produce two genetically different foetuses. They share only 50% of the DNA making them siblings who could have also been born years apart.

What Increases the Chances of Fraternal Twins?

Researchers have shown that having twins depends largely on the mother’s genetic side and if they include fraternal twins, then the chance of having them are higher.

Apart from this many other factors help increase the chances of fraternal twins. Some of them are:-

1. The mother’s age- if she is above 30 the chances are higher. This is largely due to what is known as the hormone FSH or follicle stimulating hormone which releases two eggs
2. The mother’s genetic history- if there is an occurrence of non-identical twins in the family
3. If there are twins on both sides, i.e. mother and father, then the chances go up even higher
4. Women who have BMI over 30 are more likely to have twins than the ones with a healthier BMI. Extra fat leads to higher levels of oestrogen
5. Similarly, women who are taller than the average women are more likely to have twins. A study indicated that while the average women who were 164.8 cms were more likely to conceive twins as opposed to a woman who is 161.8 cms
6. Number of earlier pregnancies and large families also increase the odds of having twins
7. In certain parts of the world, there are more twins than other. For instance, Africa has a higher number of women than other parts of the world
8. Breasting women are more likely to have twins than the women who don’t. One study found the rate twins to be 11.4% amongst breastfeeding women as compared to non-breastfeeding women for whom its just 1.1%
9. One study found that women who eat a lot of dairy products are more likely to have twins
10. Fertility treatments that boost ovulation can also lead to twins

What do Dizygotic Twins Look Like?

Do fraternal twins look alike? Yes and no. Because they share 50% DNA, they look similar just like any other brother or sister. How we look is completely controlled by chromosomes from how tall we are, to the colour of our eyes, hair and so on thereby making them look as close to alike as possible. Your twins are also born at the same time, same age and at the same rate so its normal for them to grow up together and look similar.

How will you Know that you are Pregnant with Non-Identical Twins?

A fraternal twin pregnancy can be something that you know because of intuition. Some women may even have dreams that they are pregnant with non-identical twins. You may even feel more nauseous than other pregnancies in the first trimester itself. High levels of intolerance for certain foods, smells, textures like meat, seafood, coffee can also be a sign. The most obvious one will be you will look ‘large for dates’ that is from early on itself which is a clear indicator of a twin pregnancy. Frequent urination is more magnified when you are having twins. Higher levels of hCG more, than a single pregnancy is also another factor.

Development of Fraternal Twins

A fraternal twin pregnancy week by week can be broadly divided into early and later development.

1. Early Development

In the first 8 weeks of fraternal twin pregnancy each fertilized egg has started developing into hundreds of cells having layers, attached to different sides of the womb. They have their own amniotic sac and start developing body parts and organs. By 8 weeks they have arms and legs that bend, their hearts are beating, and they start developing the nervous system

By 12 weeks they start kicking and stretching, their fingernails start growing and also eyelids over their eyes. By 16 weeks they have unique fingerprints. They also start peeing out the amniotic fluid that they start have swallowed. By 20 weeks they start getting hair.

2. Later Development –

By 24 weeks eyebrows start growing. The twins also have a full set of tooth buds for the teeth to come in after birth. By 28 weeks the twins can open eyelids, layers of fat are building under their skin and smoothing out. They can suck on their fingers. By 32 weeks the twins are fully formed with arms, legs, torso and have a full head of hair by now. They are ready to be born in a couple of weeks

What are the Risks of Having Dizygotic Twins?

One must be cognizant of the many risks involved in a twin pregnancy. Some of them are

1. Low Birth Weight is sometimes a complication of having twins
2. Intrauterine Growth Restriction can occur which slows down the rate at which your twins grow at 30 weeks. This is because the placenta cannot handle the growth of the twins
3. Pregnancy Induced Hypertension (PIH) is also higher during a twin pregnancy
4. Diabetes which is also known as Gestational Diabetes is also higher
5. Miscarriage or demise of a twin during birth is also a potential risk
6. Premature birth is also higher during a twin pregnancy

Surprising Facts about Non-Identical Twins

Some unique facts about fraternal twins you may not be aware of:

1. They can be a different gender or the same, i.e. you can have one of each gender or a set of boys or girls
2. They may not look alike since they only share 50% of the DNA and have different eye colour, stature and hair colour
3. They will have different characteristics and will not behave similarly
4. They can run in the family, and a family with a history of twins are more likely to have twins especially dependant on the mother’s side
5. They can be conceived at different times by different father, and the phenomenon is known as superfetation
6. Fraternal Twinning rates are different across different locations with Central Africa having the highest and Asia and Latin America the lowest
7. They can be had due to fertility treatments as well
8. Being pregnant with twins can put additional demand on your pregnancy

Twins are rare, and every parent should count themselves lucky if they have them. Enjoy the journey of parenthood and focus on keeping your infants healthy and happy.