In gynecological terms we speak of monozygotic identical twins zygote one originated from a single egg and sperm that subsequently divides into two and dizygotic fraternal twins two originate two eggs and zygotes different sperm. Regardless of their origin, twin pregnancies are also classified according to whether or not each fetus has its own placenta, amnion amniotic mono or bi and chorion mono-or dichorionic.
In the case of identical twins can take all possibilities. Regarding the incidence rate, 1 in 80 pregnancies are spontaneously double , being two-thirds of fraternal twins and a third of identical twins. In fact, it is thought that twin pregnancies occur in a greater proportion, but are not detected as one of the embryos stops in a very early embryonic stage.
There are both environmental factors i. Obviously the use of assisted reproductive techniques has been a key factor in increasing the incidence rate as more than one embryo is transferred, increasing fraternal twins pregnancies, specifically because they come from different zygotes. Because these twins come from one zygote, they are also known as monozygotic.
Identical twins are the same sex. About one-third of identical twins split soon after fertilisation and form completely separate twins. Like fraternal twins, these twins have separate placentas. The other two-thirds split after they attach to the wall of the womb. As a result, they share a placenta. The technical name for this is monochorionic. In a very small number of identical twins, splitting might happen even later.
In this case, both twins share an inner sac , called the amnion, in addition to sharing a placenta. The technical name for this is monoamniotic twins. For example, a twin who receives less blood from a shared placenta might weigh less at birth. Sharing a placenta means that twins share a blood supply during pregnancy.
Sometimes the blood supply is shared unequally, which can cause health problems for both twins. Women who are pregnant with twins sharing a placenta need to be checked more often than women with twins with separate placentas. Frequent checks can pick up early on any potential complications. Twins sharing an inner sac monoamniotic are also at a higher risk of complications during pregnancy because of the chance that their umbilical cords might tangle and cut off their blood supply.
These twins are checked even more closely. Medical professionals often recommend that these twins are born earlier than other types of twins. Safety and Prevention. Family Life. Health Issues. Tips and Tools. Our Mission. Find a Pediatrician. Text Size. Page Content. The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
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