Parasitic twin: what it is, why it happens and what to do

Parasitic twin: what it is, why it happens and what to do


The parasitic twin, also called fetus in fetus corresponds to the presence of a fetus inside another that has normal development, normally within the abdominal or rectoperineal cavity. The occurrence of parasitic twins is rare, estimated to occur in 1 in every 500,000 births.

The development of the parasitic twin can be identified during pregnancy by performing an ultrasound, in which two umbilical cords and just one baby can be observed, for example, or after birth, both through imaging tests and also through development. of structures that are projected outside the baby’s body, such as arms and legs, for example.

Illustrative image number 1

Why does it happen?

The emergence of parasitic twins is rare and, therefore, the reason for their appearance is not yet well established. However, there are some theories that explain the parasitic twin, such as:

  1. Some scientists believe that the emergence of a parasitic twin occurs due to changes in the development or death of one of the fetuses and the other fetus ends up encompassing its twin;
  2. Another theory says that during pregnancy, one of the fetuses is unable to form its body properly, which causes it to “parasite” its sibling in order to survive;
  3. A final theory suggests that the parasitic twin corresponds to a highly developed mass of cells, also called a teratoma.

The parasitic twin can be identified during pregnancy, but also after birth or during childhood through X-rays, magnetic resonance imaging and computed tomography, for example.

What to do

After identifying the fetus in fetusit is recommended that surgery be performed to remove the parasitic twin and thus prevent complications for the born baby, such as malnutrition, weakening or damage to organs.