Trisomy 18 (Edwards Syndrome)
Clenched fists with overlapping fingers are a characteristic feature of Trisomy 18 (Edwards syndrome), the second most common autosomal trisomy after Down syndrome. 1
Key Diagnostic Features
The fetal presentation of Trisomy 18 includes a constellation of findings that typically appear on prenatal ultrasound:
Classic Hand Positioning
- Clenched hands with overlapping fingers are among the most recognizable features, specifically described as clenched fists with overriding fingers 2, 3
- Small fingernails and underdeveloped thumbs accompany this finding 2, 3
Associated Ultrasound Findings
When Trisomy 18 is present, multiple structural anomalies are almost always evident, including: 1
- Cardiac defects (structural heart defects are among the most frequent major malformations) 1, 2
- Talipes deformity (clubfoot) of the feet 1
- Fetal growth restriction (FGR) - present in 51% overall and 89% of fetuses examined after 24 weeks 4
- Polyhydramnios 1
- Choroid plexus cysts (present in 30-50% of fetuses with Trisomy 18) 1
Timing of Detection
The specific abnormalities detected vary by gestational age: 4
- Before 24 weeks: Cystic hygromas, nuchal thickening, meningomyelocele, and choroid plexus cysts are more commonly identified
- After 24 weeks: Intrauterine growth restriction, cardiac defects, and enlarged cisterna magna become more apparent
Clinical Context
The overall prevalence of Trisomy 18 is 1/2,500-1/2,600, though live birth prevalence is lower (1/6,000-1/8,000) due to high rates of fetal loss and pregnancy termination. 2 The condition correlates positively with advanced maternal age. 2, 3
Prognosis
Understanding the natural history is essential for counseling: 2
- Approximately 50% of live-born infants survive longer than 1 week
- Only 5-10% survive beyond the first year
- Major causes of death include central apnea, cardiac failure, respiratory insufficiency, and upper airway obstruction
Important Clinical Caveat
When choroid plexus cysts are identified in isolation (without clenched hands or other structural anomalies), the risk of Trisomy 18 is much lower, with a likelihood ratio <2. 1 However, when clenched hands are present alongside choroid plexus cysts and other structural anomalies, the positive likelihood ratio increases dramatically to 66. 1