Twins share the uterus in the same pregnancy.
Twins are individuals born from the same birth in species that are not characterized by multiple births (such as the human species). In the case of animals such as cats or dogs, the term is not used. Two Latin words lead us to this concept: gemellicius , which comes from gemellus ( "twin" ).
Twins, therefore, are people who result from a single pregnancy and who, therefore, share the uterus in the same pregnancy . This means that multiple pregnancies tend to be completed in a shorter period than usual, since the space for growth of the twins is limited.
Difference between twins and twins
The notions of twin and twin often cause confusion. In some countries, both terms are used synonymously, while in others, a distinction is made between fraternal twins ( twins bivitelinos ) and twins ( twins univithelinos ).
This distinction tells us that fraternal twins are individuals originating from different eggs (with dizygotic or polyzygotic gestation), while twins originate from the same egg ( monozygotic gestation ).
The notion of twin is not used with respect to animals.
dizygotic gestation
Twins or dizygotic twins, therefore, originate from the separate but almost simultaneous fertilization of two eggs by two sperm . These twins do not share a greater genetic identity than those siblings born from separate pregnancies.
Twins can be of different sexes, allowing twin pairs to be male-male, female-female, or male-female.
At a legal level, the older brother among twins is considered to be the one who is born first (that is, the one who comes out of the mother's womb first). In this way, said twin will be the firstborn and will have the corresponding rights according to the legislation. Despite this, it should be noted that the order of birth is not linked to the order of fertilization, but to the place of growth of each individual with respect to exit from the uterus.
Myths about twins
As explained in previous paragraphs, the terms twin and twin are not always used clearly, and this leads to certain confusion. On the other hand, myths have also been created regarding the relationships between siblings born from the same pregnancy, such as that they have a psychic connection comparable to telepathy, which has not been scientifically proven.
Regarding the influence of genetic inheritance on whether twins are born, it is correct to ensure that the first case has been proven by medicine and can be anticipated by studying the family history and certain physiological characteristics of the mother. Regarding the probabilities of having twins, there is no reliable evidence that allows us to determine them, although it is not ruled out that it may be possible in the future.
Many people believe that in a twin pregnancy there is a single placenta and a single amniotic sac ; However, this depends on the day on which the egg divides, and the possibilities are diverse (one placenta and two amniotic sacs, two placentas and one amniotic sac, etc.). It is worth mentioning that if the embryo divides around day ten of gestation, then both organs will be shared.
One of the most widespread myths regarding pregnancy with twins is that they do not feel the bond known as the twin bond . Various studies have proven that, since a person shares the beginning of their life with their twin brother in a very similar way to what happens with twins, they also experience a deep understanding on a psychological level.
To summarize the differences between twins and twins, we can say that
- Twins : They are also known as identical twins ; they share 1 egg and 1 sperm, which divides; They have the same gender ; Their physical resemblance is very high, and they can become identical; They share all the genes.
- Twins : They are also known as fraternal twins ; They are born from 2 eggs and 2 different sperm; they may or may not have the same gender; They can look as similar as two brothers from different pregnancies; They share half of the genes.