Teratomas of embryonal origin are most often found in babies at birth, in young children, and, since the advent of ultrasound imaging, in fetuses. The most diagnosed fetal teratomas are sacrococcygeal teratoma (Altman types I, II, and III) and cervical (neck) teratoma. Because these teratomas project from the fetal body into the surrounding amniotic fluid, they can be seen during routine prenatal ultrasound exams. Teratomas within the fetal body are less easily seen with ultrasound;  for these, MRI of the pregnant uterus is more informative. Complications
Teratomas are not dangerous for the fetus unless either a mass effect occurs or a large amount of blood flows through the tumor (known as vascular steal). The mass effect frequently consists of obstruction of normal passage of fluids from surrounding organs. The vascular steal can place a strain on the growing heart of the fetus, even resulting in heart failure, thus must be monitored by fetal echocardiography. Teratomas can cause an autoimmune illness called  N-methyl-D-aspartate (NMDA) receptor encephalitis. In this condition, the teratomas may contain B cells with NMDA-receptor specificities.After surgery,  a risk exists of regrowth in place, or in nearby organs. Pathophysiology
Teratomas belong to a class of tumors known as nonseminomatous germ cell tumor. All tumors of this class are the result of abnormal development of pluripotent cells: germ cells and embryonal cells. Teratomas of embryonic origin are congenital; teratomas of germ cell origin may or may not be congenital.
In particular, risk of aneuploidy is increased by tobacco smoking, and occupational exposure to benzene, insecticides, and perfluorinated compounds. Increased aneuploidy is often associated with increased DNA damage in spermatozoa. Structural abnormalities
When the chromosomes structure is altered, this can take several forms:
Deletions: A portion of the chromosome is missing or has been deleted. Known disorders in humans include Wolf–Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder. Duplications: A portion of the chromosome has been duplicated, resulting in extra genetic material. Known human disorders include Charcot–Marie–Tooth disease type 1A, which may be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17. Inversions: A portion of the chromosome has broken off, turned upside down, and reattached, therefore the genetic material is inverted. Insertions: A portion of one chromosome has been deleted from its normal place and inserted into another chromosome. Translocations: A portion of one chromosome has been transferred to another chromosome. There are two main types of translocations:
Reciprocal translocation: Segments from two different chromosomes have been exchanged. Robertsonian translocation: An entire chromosome has attached to another at the centromere - in humans, these only occur with chromosomes 13, 14, 15, 21, and 22. Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without the loss of genetic material.