Trisomy 18, also known as Edwards syndrome, is a condition that is caused by an error in cell division, known as meiotic disjunction. When this happens, instead of the normal pair, an extra chromosome 18 results (a triple) in the developing baby and disrupts the normal pattern of development in significant ways that can be life-threatening, even before birth. A Trisomy 18 error occurs in about 1 out of every 2500 pregnancies in the United States and 1 in 6000 live births. The numbers of total births is much higher because it includes significant numbers of stillbirths that occur in the 2nd and 3rd trimesters of pregnancy.
Unlike Down syndrome, which also is caused by an extra chromosome, the developmental issues caused by Trisomy 18 are associated with more medical complications that are more potentially life-threatening in the early months and years of life. Studies have shown that only 50% of babies who are carried to term will be born alive, and baby girls will have higher rates of live birth than baby boys.
At birth, intensive care admissions in Neonatal Intensive Care Units (NICU’s) are routine for infants with Trisomy 18. Again, baby boys will experience higher mortality rates in this neonatal period than baby girls, although those with higher birth weights do better across all categories.
Some infants will be able to survive to be discharged from the hospital with home nursing support to assist with care by the parents. And although 10 percent or more may survive to their first birthdays, there are children with Trisomy 18 that can enjoy many years of life with their families, reaching milestones and being involved with their community. A small number of adults (usually girls) with Trisomy 18 have and are living into their twenties and thirties, although with significant developmental delays that do not allow them to live independently without full time caregiving.