What are nocturnal twins

Twins, multiples: what exactly are twins?

Last change:
Next update of Till von Bracht • Medical editor

Our content is based on well-founded scientific sources that reflect the currently recognized state of medical knowledge. We work closely with medical experts.

Learn more

Multiples are two (twins) and more babies who grow up together in the womb.

  • There are identical (monozygous) and
  • fraternal twins (dizygote).
  • Different combinations of identical and dizygotic babies can occur in triplets and more.

Identical twins

Identical twins arise when A single one fertilized egg divides at a very early stage in such a way that two cell nuclei with identical genetic material arise. If the egg divides at a later stage (rarely), Siamese twins can occur. The egg cell usually divides very early, so that the embryos, which are now independent of one another, migrate separately to the uterus and implant themselves there in their own fruit cavity and with their own placenta.

Identical twins rarely share a common fruit cavity and placenta. In this case, the pregnancy must be carefully monitored, as there is an increased risk of an embryo being undersupplied.

Identical twins always have the same sex and are completely identical in their genetic makeup. As a result, they are largely the same both physically and in terms of character. Studies on pairs of twins who were separated immediately after birth for a wide variety of reasons have shown this.

Dizygotic twins

Dizygoti twins result from the fertilization of two egg cells, which can come from one or both ovaries. Dizygoti twins therefore always have their own fruit cavity and placenta. Fraternal twins can be of the same or different sex. They differ in their genetic makeup and behave physically and mentally like ordinary siblings.

Triplets & more

Triplets and other multiples can arise from a combination of monozygotic and dizygotic embryos. It is possible that two egg cells are fertilized and one of these egg cells further divides into dizygotic twins. It is also possible for three or more individual eggs to be fertilized.