At seven months pregnant, Mónica Vega discovered she had two umbilical cords inside her.
Doctors diagnosed her unborn daughter with a rare condition called "fetus-in-fetu" - where a malformed fetus is found in the body of its twin.
Fetus in fetu (or foetus in foetu) is a developmental abnormality in which a mass of tissue resembling a fetus forms inside the body, Wikipedia reported.
There are two theories of origin concerning "fetus in fetu". One theory is that the mass begins as a normal fetus but becomes enveloped inside its twin. The other theory is that the mass is a highly developed teratoma - a tumour made up of several different types of tissue, such as hair, muscle, teeth, or bone.
"Fetus in fetu" is estimated to occur in one in 500 000 live births.