Babies with trisomy 18 have three copies of chromosome 18 and have severe intellectual disabilities and birth defects typically involving the heart, brain, and kidneys. Babies with trisomy 18 can also have visible birth defects such as an opening in the lip (cleft lip) with or without an opening in the roof of the mouth (cleft palate), a small head, clubbed feet, underdeveloped fingers, and toes, and a small jaw. Unfortunately, most pregnancies with trisomy 18 will miscarry. If born alive, most affected babies with trisomy 18 will pass away within the first few weeks of life. About 10 percent survive to their first birthday. Trisomy 18 occurs in approximately 1 in 3,000 live births.