A sacrococcygeal teratoma / SCT is a tumor that develops in a baby in utero. It appears in the lower back and buttocks of a baby at the base of the tailbone (coccyx). Some tumors are diagnosed in utero, others at birth.

Sacrococcygeal teratomas / SCTs are rare, occurring in about one in 35,000-40,000 births. However, in newborns with tumors, they are one of the most common types to develop. Females are four times more likely than males to be affected by these tumors. The cause of SCT is not known.

An SCT is a tumor that grows from germ cells, which are the same cells that give rise to a sperm or an egg. These tumors are made up of cells that can resemble any type of tissue in the body such as bone, nerve, teeth, muscle, and so on. These tumors can grow fast and become very large. They can be located both inside and outside the pelvis of a baby.

If your baby develops this type of tumor, you likely will not experience any symptoms early in the pregnancy. Later, the baby can develop illness quite rapidly and become very sick. In some instances, the mother can develop “maternal mirror syndrome” and become very sick as well.

Tumor Classification 

Sacrococcygeal teratomas / SCTs are grouped according to the amount of tumor present inside and/or outside the baby.

  • Type I tumors are completely external (outside the body) and easily identified during a prenatal ultrasound or at birth.
  • Type II tumors are mostly external but a portion is inside the body.
  • Type III tumors are mostly internal but a portion is outside the body.
  • Type IV tumors are completely inside the baby’s body and cannot be viewed externally. They are usually recognized late, and they have the highest rate of malignancy.

Most SCTs are benign (not cancerous).