Trisomy 18, also known as Edwards syndrome and trisomy E, is the second most common fetal aneuploidy, after trisomy 21 (Down syndrome). Trisomy 18 is the condition of having three copies, rather than two, of chromosome 18. Trisomy 18 can be full, partial, or mosaic. 80-85% of trisomy 18 cases are considered full, 10% of cases are considered mosaic, and 5% of cases are considered partial. The incidence rate of trisomy 18 ranges between 1 in 3,000 and 1 in 7,000 live births.
The risk of trisomy 18 can be assessed in the first and second trimesters via ultrasound and maternal serum screenings. A diagnosis can be made through fetal karyotype tests like amniocentesis or chorionic villus sampling (CVS).
Trisomy 18 often presents in conjunction with other abnormalities such as central nervous system anomalies, congenital heart defects like atrial septal defect (ASD) and ventricular septal defect (VSD), choroid plexus cysts, intrauterine growth restriction (IUGR), and hand anomalies like clenched hands and overlapping fingers.
The life expectancy of a baby born with trisomy 18 varies. 55% to 65% of babies born with trisomy 18 die within the first week of life; however, 5% to 10% of infants are alive at one year of age. While these infants do grow, mature, and learn, long-term survivors experience extensive hospital stays, cardiac and respiratory complications, difficulty feeding, hearing loss, and developmental delay. Female babies diagnosed with trisomy 18 are more likely to be born alive and survive longer than males. The median life expectancy for a baby boy born with trisomy 18 is 1 to 2 months, and the median life expectancy for a baby girl born with trisomy 18 is 9 to 10 months.
The reoccurrence risk for full trisomy 18 is 1% or the maternal age-related risk, whichever is greater. In trisomy 18, the extra chromosome is almost always inherited from the mother. Parental genetic testing is recommended prior to a subsequent pregnancy.