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. Some tumors are diagnosed in utero, others at birth. 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.