TWIN
See also: Twin (homonymy)
Literally, the twin term refers to all the Individu S (or one of those
Ci) which divided same the Utérus and which were born the same day. The triplets (or quadrupled) are thus 3 (or 4) jumeaux.
In the language running, one usually speaks about twin to indicate a birth double.
There exist documented cases where one of the twins was born later that his “joint tenant”.
There are a physiological limit, volume and weight for example, so that a mother can carry. For this reason, it is notably rarer than this one can carry out a multiple pregnancy in the long term. For health reasons in the mother, a pregnancy of twins must be more followed than a “traditional” pregnancy. On the other hand, the very premature childbirth has important consequences on the health of the children. But the Obstétricien S also supervise a twin pregnancy near to the term and can sometimes privilege a Naissance with 2 weeks in advance.
Types of twins
Twins dizygotes or fraternal twins
This situation occurs when two ovules fertilized by 2 spermatozoa nidifient on the walls of the uterus. This situation generally occurs in the same menstrual cycle. The two ovules form then two zygotes different and the twins thus designed are known as dizygotes (in genetics, one will say hétérozygotes).The genetic relationship between twins dizygotes, which develop thanks to two Placenta S separated, is the same one as that between two newborns of two different pregnancies. It can thus be different sexes.
All these pregnancies are bichoriales biamniotic (2 placentas; 2 amniotic cavities).
The genetic predisposition which supports their arrival is to be sought maternal side, since the future dad does not influence of anything double original ovulation.
Twins monozygotes or identical twins
This situation occurs when an ovule is fertilized by a spermatozoon, and that the zygote which results from this separates into two, thus forming two Embryon S which has same genetic inheritance.If the embryo divides less than three days after fecundation, that will lead to a twin pregnancy bichoriale (2 placentas) biamniotic (2 amniotic cavities) as for the twins dizygotes. A third of the twin pregnancies is biamniotic pregnancies monozygotes bichoriales. In spite of their separated growths, it is in this case of figure that the twins resemble each other more the birth (weight and size).
If the embryo divides between 3 and 6 days there will be only one placenta (monochorial) but two amniotic cavities (diamniotic). In this case there can be a difference of food between the two twins during the pregnancy and thus of the variations of size and weights to the birth which will attenuate during the growth.
If the scission of the zygote is carried out after the formation of the amniotic cavity the pregnancy is monochoriale monoamniotic. The twins divide the same amniotic cavity. If the scission does not take place, that leads to the training of Siamese babies.
The twins monozygotes are often very physically resembling. By taking age, the twins monozygotes are different following the personal choices and with the experiments from life. The schooling is an important step in this field of differentiation.
For science, they make it possible to highlight mechanisms epigenetic S as of the differences of Méthylation of the DNA which appear during the life.
-
See also Twin monozygotes
Semi-monozygotes twins
It happens that the polar Globule is fertilized at the same time as the ovule, that will give rise to semi-monozygotes twins. They share the genetic code brought by the mother, whereas they have a code different on the paternal side. They can thus be different sexes and will develop in a pregnancy which will be dichoriale diamniotic. It is necessary to make a research in the ARN mitochondrial to distinguish them from the twins dizygotes in molecular biology.Internet sites
: Federations of associations of twins in France : The French-speaking Community on the twins and binoculars
Typology of the twin pregnancies
Biamniotic pregnancy bichoriale
Two amniotic placentas and two pockets
Biamniotic pregnancy monochoriale
An amniotic placenta and two pockets
Monoamniotic pregnancy monochoriale
A placenta and an amniotic pocketRare pregnancy. 1% of the monozygotes. Mainly girls.
Monitoring of the twin pregnancy
It will be a pregnancy with a more significant number of echography and a regulation of rest to avoid the prematurity which touches 50% of the births.
Complications of the twin pregnancy
Common complications
Prematurity and delay of growth. A follow-up in a maternity which can too early accommodate newborns and hypotrophes is recommended.
Phantom twin
Certain echography show the presence of several Fœtus in the first weeks of pregnancy, but some do not arrive in the long term for various reasons. At this time, one speaks about phantom twin. In scientific terminology, one names them " papyrus".
Specific complications
Monoamniotic pregnancy monochoriale
Siamese twins
The Siamese twins or Siamese twins are twins homozygotes who have welded part of their body. This situation, presents in 1 case on 100 000, occurs when the zygote of these twins cannot divide completely. They are mainly girls.
Parasitic twin
Sometimes, when compared with the other, one of the twins does not manage to grow sufficiently quickly. In this case, it behaves a such parasite for the other. In pathology, it is sometimes very difficult to distinguish from a Tératome. It is also a rare situation. One however detects a case, that of an Indienne little girl, who has 4 arms and 4 legs
Human twins
Historically, approximately 1 human pregnancy out of 80 (1.2 %) gives rise to twins. The percentage of twins dizygotes varies according to the ethnicities: the least frequent in Asia, most frequent in Africa. It is in the ethnos group of Yorubas that the frequency is highest. The use with large scales of the drugs of fertility which cause a hyperovulation (several ovules emitted simultaneously by the mother) seem the cause of what some call a “epidemic of multiple births”. With the the United States, in 2001, the rate of birth of the twins reached 3 %, historical records.
Multiple births
When there is birth of three babies, triplets are spoken; four, quadrupled; five, quintuplets; six, sextuplets; etc Before the advent of the drugs of fertility, the birth of triplets was rare (approximately 1 by 8000 births) and that of quadrupled, quintuplets, etc, definitely rarer (the newspapers brought back such events because, precisely, of their scarcity).Prematurity is a frequent complication. The intermediate duration of the pregnancy is 35 weeks for the twins, 32 weeks for the triplets and 30 weeks for quadrupled.
Determining factors
The causes of the gemellity monozygote are still unknown today.The probability of pregnancy with twins dizygotes is supported by the following factors at the Femme:
- It is of African descent .
- It is old between 30 and 40 years.
- It is larger and more door that the average.
The women who take drugs of fertility have the most chances to have multiple pregnancies (25 to >30%). In much case they are indeed pregnancies induced by a hormonal treatment or by FIV (In vitro fertilization).
Studies on the twins
These studies are interested in the medical aspect , psychological Génétique or . They are made with an aim of discriminating the influence of genes of that of the Environnement.
Records
- Spain: birth the December 30th 2006 of two twin children of a 67 years old mother to Barcelona, thus beating the record of age of Procreation. The mom “profited from a hormonal treatment and fecundation in vitro abroad” according to the spokesperson of the hospital where it was confined.
Twins in the animals
The multiple births are common at the Mammifère S.The known record (source Guinness World Records) is of 24 small in only one range: