When an ultrasound is performed to confirm the pregnancy, it is time to also know the number of babies that are on the way, which will significantly influence the controls of pregnancy, childbirth and, of course, the lives of children and children. parents.
Not all multiple pregnancies are the same but, depending on the number of fertilized ovules and when the zygote division occurs, there are different types of twins.
Before starting and given the frequent confusion between twins and twins it is convenient that we take a look at the definition of twins. The twins are "the brothers born from the same birth." That is, every pregnancy of more than one baby is considered a twin pregnancy, whether they are twins or twins.
Let's look at the different classifications that are known:
Bicigotic or biviteline twins (twins)
They represent 70% of twin pregnancies. They are the result of two ovules fertilized by two sperm They have formed two zygotes. They are two different gestations that develop at the same time. Each is implanted independently, within its gestational sac with its own placenta and its own amniotic bag.
AdvertisingThe development of bicigotic or biviteline twins is usually greater than that of univiteline twins.
For this to happen there must have been two ovulations in the same menstrual cycle, either two ovules from the same ovary or one ovule from each ovary.
Being the fertilization of two ovules and two sperm cells, the genetic load is different, which means that children may or may not be of the same sex. Therefore, they are not identical, being what we know as twins. Of every 100 twin pregnancies, half are of different sex, and of those of the same sex, half are 2 men and half 2 women.
Monozygotic or Univiteline Twins
It is less frequent than the previous one. They represent 30% of twin pregnancies and their incidence is approximately one pair of twins every 250 births. Unlike the previous ones, the zygote is formed by the union of an ovule and a sperm that after fertilization is divided to create two embryos. The division of the zygote is considered a fortuitous event, a “biological accident” in which race, mother's age or inheritance do not influence.
Babies that arise from this fertilization carry the same genetic information, so they are always of the same sex, which is known as identical twins, which although they are not completely, their physical similarities are usually very large.
Depending on when the zygote divides, we will have different types of monozygotic or univiteline twins.
- 1) Bicorials and biamniotics: when the zygote division occurs within 3 days after fertilization. Each embryo grows inside its own amniotic bag and feeds on its own placenta.
- 2) Monocorials and biamniotics: when the division of the zygote occurs between the fourth and seventh day after fertilization. They share the same placenta but each one grows in its own amniotic bag. They represent 90% of monozygotic twin pregnancies.
- 3) Monocorial and monoamniotic: These are very rare cases. It happens when the division of the zygote occurs late, between 7 and 13. day after fertilization. They share placenta and amniotic bag, the embryo being the only thing that divides. Complications tend to be more frequent in this type of pregnancy.
Within this last group of monochorionic and monoamniotic twins are the pregnancies of Siamese or United Twins, which happens when the zygote division occurs after the 13th day after fertilization. The division is incomplete and they are united by some part of their bodies (thoracophagous, united by the thorax; pigópagos, united by the buttocks and craniopagos, united by the head)
Triple, quadruple, quintuple twin pregnancy ...
All are called twin pregnancies even if the number of embryos is greater than two. As we have said before, the twins are those born from the same birth and can be two, three, four, five, six and there have even been exceptional cases such as septuplets in Egypt.
Inside of the triple twin pregnancy There are in turn three types depending on the amount of fertilized eggs.
1) It may have been the fertilization of a single ovule that was divided into two and one of them then divided again into two. They are known as identical triplets, because they share the same genetic material and of course, they are the same sex.
2) Two eggs fertilized by two sperm cells and one of them was divided into two, resulting in three children. The two children born of the same ovule and sperm share genetic material and would have the same sex (what is usually called twins), while the other can be of different sex (what is usually called twin).
3) Three ovules fertilized by two sperm (tricigotic twins). As in the case of visigotic twins, each one has its own genetic load, its own amniotic and placenta bag. They seem like any brother with the difference that they are gestated at the same time.
He quadruple twin pregnancy, is the result of two ovules that in turn were divided into two, or 3 ovules, two independent and one that in turn is divided into two, or much more strange if we talk about natural fertilization, four ovules independent fertilized by four sperm in the same cycle.
Thus, as the number of embryos resulting from the most exceptional divisions increases are pregnancies. We could continue with five, six or more.
The combinations can be many, but I hope this classification of types of twins may serve to clarify some doubts about multiple births.
