One of the unusual cases is the phenomenon of the vanishing twin. This situation sometimes occurs during multiple pregnancies. The mother's body rejects one or more embryos, arranging a selective miscarriage of all fetuses except one chosen one, and they leave her body along with obstetric hemorrhages.
Vanishing twin syndrome can only occur if a woman has a multiple pregnancy. It is rarely observed during natural conception; most often this phenomenon occurs during artificial insemination with the implantation of several embryos.