Predictive value of fetal ultrasonography in the diagnosis of a lethal skeletal dysplasia

Background. Certain ultrasonographic findings identified in a fetus suspect ed of having a skeletal dysplasia may be predictive of a lethal outcome. Methods, We evaluated 27 fetuses suspected of having a skeletal dysplasia u sing targeted ultrasonography between 16 and 31 weeks' gestation. Clinical examination and skeletal radiography were done after delivery. Results. A skeletal dysplasia was confirmed and a diagnosis established in all hut one case. The skeletal dysplasia was lethal in 23 cases and, in eac h case, the outcome was accurately predicted prenatally; however, three of the infants survived several months. In II of the 23 cases (48%), the speci fic diagnosis was correctly determined before birth. Ultrasonographic findi ngs nor considered to reflect a lethal outcome, were accurately predicted i n two other cases. In an additional two, sonographic examination suggested a lethal osteochondrodysplasia, though both survived. Findings consistent w ith a lethal skeletal dysplasia included a femur length < 1st centile, comb ined with either a bell-shaped thorax, decreased bone echogenicity, or both . Using these criteria provided a positive-predictive value for neonatal de aths of 80% (20/25), and 92% (23/25) if the three that died in infancy were included. Conclusions. In the fetus suspected of having a skeletal dysplasia, certain findings on targeted ultrasonography frequently are predictive of a lethal outcome; the ability to predict this appears greatest when more than one o f these abnormalities is present.