Complications of twin pregnancy

Complications of twin pregnancy
Vanishing twins : Vanishing twin Researchers suspect that many more pregnancies start out as multiples than go to term that way. Early obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes. This is known as vanishing twin syndrome.
Conjoined twinsMain article: Conjoined twin Conjoined twins are monozygotic twins, whose bodies are joined together at birth. This occurs where the single zygote of identical twins fails to separate completely. This condition occurs in about 1 in 100,000 pregnancies.
Parasitic twins
Sometimes one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. One fetus acts as a parasite towards the other.
Sometimes the parasitic twin just becomes an almost indistinguishable part of the other.
A chimera is a person who is a completely normal human with no extra parts, but some of the parts actually came from his or her twin. A chimera may arise either from identical twin fetuses (where it would be impossible to detect), or from dizygotic fetuses, which can be identified by chromosomal comparisons from various parts of the body. The number of cells derived from each fetus can vary from one part of the body to another, and often leads to characteristic mosaicism skin colouration. A chimera may be a hermaphrodite, composed of cells from a male twin and a female twin.