Twin
From Simple English Wikipedia, the free encyclopedia
When a mother has two children at the same time (in the same pregnancy), this pair is called a twin. The mother can be a human being or any other animal.
[edit] Twin pregnancy in people
Human twins are two people that shared the uterus during a single pregnancy, and one is normally born quickly after the first. Because of the size of the uterus, multiple pregnancies are less likely to last the full 38 weeks than most single birth pregnancies. On average, they last 35 weeks. This also means about 50% of twins is born prematurely.
[edit] Variations
There are five variations of twinning that occur commonly in the world. The three most common variations are all fraternal, meaning the two twins are not from the same egg:
- (1) male-female twins are the most common result, at about 40% of all twins born;
- (2) female fraternal twins (sometimes called sororal twins), about 20%;
- (3) male fraternal twins, about 20%.
The last two variations are identical twins, which means they come from one single egg that split later:
- (4) female identical twins (about 10%) and
- (5) (least common) male identical twins (about 10%).
[edit] Other animals
Twinning is common in many other animals, such as cats, sheep, and ferrets. Twinning occurs in cattle about 1-4% of the time, and research is underway to improve the odds of twinning, which can be more profitable for the breeder if complications can be sidestepped or managed.
