Identical or Fraternal Twins: What’s the Difference?


news of a pregnancy twin can cause an initial surprise followed by a double dose of happiness and multiple emotions, but it also tends to raise a lot of doubt. An ultrasound will determine if there is one baby or several. When it comes to two babies, there can usually be confusion as they can be identical or fraternal twins.

The difference between both types of multiple pregnancies lies in: the number of fertilized eggs or when the same zygote that is formed during pregnancy has proceeded to divide to become two embryos. We analyze what these types of twin pregnancies look like.

identical twins

In singleton pregnancies, the zygote forms after the union of a single egg with a sperm and this divides after fertilization to form two identical embryos. The identical twins share their genetic makeup so physically they are almost identical. It is a fact that occurs in very few cases, between 25%.

There are different types of identical twins depending on when the zygote divides:

  • Bichorionic and Diamniotic: occurs 3 days after conception. The embryos are nourished by a single placenta and each has its own amniotic sac.
  • Monochorionic and monoamniotic: It occurs between the seventh and thirteenth day and where the embryos share the same placenta and amniotic sac. It is when a division of exactly the same cells has taken place.

Univiteline or biviteline twins

Interesting Facts About Identical Twins

In this type of distribution, the case of disappearing twins in which one of the embryos does not develop and is eventually absorbed by the mother, by her own twin brother or even by the placenta. It has been observed that in the second trimester two fetuses appear, and in the subsequent ultrasound one of them has disappeared.

Another curious and very rare fact is the so-called “Inverse situation” where babies are born as twins and the organs are formed in the opposite way. They may even do opposite things in their lives (reverse psychology), while one is left-handed, the other right-handed, or they may even sleep in reverse.

identical twins

A twin pregnancy occurs when: two eggs are fertilized by two different sperm cells and form two zygotes in two different sacs. It usually occurs in 70% of twin pregnancies. Each egg implants independently in the uterus, in her gestational sac and her own amniotic sac and placenta. This type of twin is the most common. Fraternal twins are commonly called Twins.

The chance of a twin pregnancy increases when two zygotes are implanted in the mother’s uterus at the same time. There is a curious fact in the fraternal twins, since they can be of different sexes. Out of every 100 pregnancies with this characteristic, they are usually of different sexes or can coincide as two males or two females.

case of twins

Are Fraternal Twins the Same or Different?

the twins have different genetic information so they are not physically identical. They may even be of a different gender, as we discussed. Their physical resemblance is similar to that of two regular siblings although there are instances where they can also be born very similar but they will not be mirror twins. These twins are also known as fraternal or dizygotic twins.

How do you know if they are identical twins or fraternal twins?

Sometimes it’s hard to tell if twins are identical or identical. If the babies are of the opposite sex, they are identical twins. since, identical twins they are always of the same sex.

If the babies are of the same sex, they become twins. singles if they share the outer bag or both bags. This data can be formalized with routine ultrasound and analyzing all this data.

When in doubt, the doctor performs A blood test obtain blood group. If the blood type is different they will be twins. If the results of the analyzes are not conclusive, the last option is to perform a To test of DNA.

Differences Between Identical and Fraternal Twins

To provide more curiosity between these two types of twin pregnancies, we will conclude with some clear differences that will be much more significant and convincing.

The gender of the babies

Before birth, the sex of unborn babies can be detected. If the sexes are different, there is no doubt that they are twins. or fraternal twins. But if they are of the same sex, there will be doubt as to whether they can be identical as the twins can also be of the same sex. We should analyze by ultrasound whether they share the amniotic sac or not.

Univiteline or biviteline twins

Amniotic sac and placenta

In twin pregnancies, since each of the embryos is made with its own egg and sperm, they will logically be implanted in the uterus independently. In this way, each will create its own amniotic sac and placenta.

In the case of identical twins, there are cases that can be very different:

  • It may happen that the embryos they usually share the same amniotic sac and placenta, this usually happens between days 7 and 13 after conception. But even if it does happen, the future may have implications for their birth, as they may have conjoined twins (when they are born physically united with each other) or transfusion-transfusion syndrome may occur.
  • At the time of division of the zygote, the embryos are formed and each can develop their own amniotic sac and their own placenta.
  • Between the fourth or seventh day the babies they can have their own amniotic sac, but they share the same placenta. This is a situation that usually occurs in 90% of cases.

Other details that make them stand out is when they are born and their physical appearance is examined. If they are clearly identical, that’s when they were born with the same genetic load and that’s why they are identical twins. On the other hand, they can be twins, but in this case they share 50% of the DNA and are clearly distinguishable, although there are cases where they can be very similar. They also do not share the same blood type.

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Author: pauadu

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