They have a small head, with a sloping forehead. Usually, there are major structural problems with the brain which are diagnosed shortly after birth. Often, the front of the brain does not divide properly, resulting in a condition called holoprosencephaly. This can cause changes in the development of the baby s face, where the eyes are close set, or the nose or nostrils are underdeveloped. Cleft lip and cleft palate are present in 60 to 80 percent of babies with trisomy 13.
Eye problems are common and the ears are low-set and unusual in shape.
The feet may have prominent heels. In 80 percent of the cases, there are other health problems present at birth. In males, the testes fail to descend into the scrotum. Females may have an abnormally shaped uterus, called a bicornuate uterus. Since trisomy 18 and trisomy 13 each have a unique group of characteristics, a physician may be able to determine simply by physical examination whether a baby has trisomy 18 or 13.