Trisomy 18
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Description
Trisomy 18, or Edward’s syndrome, occurs when a human receives an extra copy of chromosome 18 at conception. Chromosomes are the genetic material that determines the growth and functions of human beings. Usually, humans have 2 copies of each chromosome. Humans with Trisomy 18 have 3 copies of chromosome 18. Trisomy 18 can cause slow development during pregnancy, heart and kidney defects, breathing and feeding problems, and hearing difficulties. Other characteristics of Trisomy 18 include intellectual disability, low birth weight, a small head, jaw, and mouth, and clenched fists with overlapping fingers. Trisomy 18 occurs in 1 in 3,000-7,000 live births and is not inherited in most cases.
Screening and Diagnosis
Trisomy 18 is diagnosed prenatally by amniocentesis or chorionic villus sampling (CVS). A positive prenatal biochemical screen (e.g., Quad test), ultrasound scan, or NIPT/NIPS screen indicates the chance of a possibly higher risk for this abnormality. NIPS screens for T18 carry a high false-positive rate (the result says there is a high risk, but there is no risk at all). Therefore, follow-up confirmatory diagnostic testing is recommended to confirm any positive T18 screening result to confirm the risk (a diagnostic test such as amniocentesis, CVS, or newborn screening). Amniocentesis tests the amniotic fluid during the second or third trimester of pregnancy and CVS tests the placenta to confirm a Trisomy 18 diagnosis. These diagnostic tests pose a 1 in 500 risk of miscarriage.
Treatment/Prognosis
Trisomy 18 is a life-limiting condition that carries a significant risk of mortality and severe disability. About 10 percent of babies live through the first year of their life. The prognosis for children with Trisomy 18 depends on the associated medical conditions and may include cardiac and orthopedic surgery and feeding assistance to manage the baby’s symptoms to improve the quality and length of the baby’s life after birth. The literature reporting on families who pursue medical support for their infants who live beyond 3 months demonstrates that these children, while they may undergo more medical procedures than other children, are valued family members, that they are generally happy, and they have a positive impact on siblings. In addition, families who chose to continue the pregnancy with a child with Trisomy 18 report they would continue a future pregnancy with a child with Trisomy 18.
Medical advances are continually improving treatment options and outcomes so consulting with specialists and major children’s hospitals may be beneficial to find the best possible care.
Palliative care programs are available to support infants and their families for parents who may not be able to pursue medical interventions for their child with a life-limiting condition. They may ask their medical team for more information about perinatal palliative care programs that are available to them.
Sources:
Glossary of Types of Infant Loss - Google Docs
Trisomy 18 | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program (nih.gov)
Trisomy 18 (cincinnatichildrens.org)
Edwards Syndrome (Trisomy 18): Genetic Condition, Symptoms & Outlook (clevelandclinic.org)
Trisomy 18 (Edwards Syndrome): Types & Diagnosis | SSM Health
Trisomy 18 (cincinnatichildrens.org)
Amniocentesis - Carrying To Term
Trisomy 18 | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program (nih.gov)
Malloy C, Wubbenhorst MC, Lee TS. The perinatal revolution. Issues Law Med. 2019 Spring;34(1):15-41. PMID: 31179670.