Identical triplet brothers at graduation. Identical triplets are very rare. A<unk>  is the culmination of one<unk>  pregnancy, wherein the mother gives birth to two or more babies. A term most applicable to vertebrate species,<unk> s occur in most kinds of mammals, with varying frequencies. Such births are often named according to the number of offspring, as in twins and triplets. In non-humans, the whole group may also be referred to as a litter, and<unk> s may be more common than single births.<unk> s in humans are the exception and can be exceptionally rare in the largest mammals. A<unk>  pregnancy may be the result of the fertilization of a single egg that then splits to create identical fetuses, or it may be the result of the fertilization of<unk>  eggs that create fraternal ("non-identical") fetuses, or it may be a combination of these factors. A<unk>  pregnancy from a single zygote is called monozygotic, from two zygotes is called dizygotic, or from three or more zygotes is called polyzygotic. Similarly, the siblings themselves from a<unk>  may be referred to as monozygotic if they are identical or as dizygotic (in cases of twins) or polyzygotic (for three or more siblings) if they are fraternal, i.e., non-identical. Each fertilized ovum (zygote) may produce a single embryo, or it may split into two or more embryos, each carrying the same genetic material. Fetuses resulting from different zygotes are called fraternal and share only 50% of their genetic material, as ordinary full siblings from separate births do. Fetuses resulting from the same zygote share 100% of their genetic material and hence are called identical. Identical twins are always the same sex.
Multiple birth
Male lactation
Male pregnancy
Abortion in Europe
History of abortion
Preterm birth
History of birth control
Sexual activity during pregnancy