Trisomy 21 in newborn infants: chest radiographic diagnosis.

Chest radiographs of 30 infants with trisomy 21 and 881 unaffected infants were evaluated for the following findings common in trisomy 21: multiple manubrial ossification centers, 11 rib pairs, and a bell-shaped chest. Radiographs were obtained in the first 48 hours of life. Of the 881 unaffected infants, 85 (9.6%) exhibited multiple manubrial ossification centers; 46 (5.2%), 11 rib pairs; and 208 (23.6%), bell-shaped chest. Of the 30 infants with trisomy 21, 24 (80%) exhibited multiple manubrial ossification centers; ten (33%), 11 rib pairs; and 24 (80%), bell-shaped chest. The probability of trisomy 21 in routinely radiographed newborn infants is 0.05% when none of the three findings is present, 1.6% with multiple manubrial ossification centers alone, 0.2% with 11 rib pairs alone, and 0.7% with bell-shaped chest alone. The probability of trisomy 21 increases in patients with two findings and reaches 58.4% in patients with all three findings.