Suspected skeletal dysplasias: Femur length to abdominal circumference ratio can be used in ultrasonographic prediction of fetal outcome, , ,

OBJECTIVES: Skeletal dysplasias are a group of bone growth disorders, some of which can be recognized prenatally. Certain types of skeletal dysplasias result in a lethal fetal outcome. The ability to predict this outcome prenatally would be important in counseling parents. This study evaluated the ratio of femur length to abdominal circumference as a predictor of fetal outcome in cases of suspected skeletal dysplasia. STUDY DESIGN: This 3-year retrospective study identified 18 cases of prenatally suspected skeletal dysplasia from a population of approximately 35,000 fetuses undergoing prenatal ultrasonography. The femur length/abdominal circumference ratio was calculated and compared with fetal-neonatal outcomes and diagnoses. RESULTS: Eighteen cases of suspected skeletal dysplasia were identified, and the femur length/abdominal circumference ratio was found to be a good predictor of fetal outcome independent of gestational age. A ratio <0.16 resulted in a lethal outcome in nine of nine cases. Conversely, a ratio ≥0.16 resulted in a diagnosis of a nonlethal form of skeletal dysplasia or a diagnosis that ruled out any form of skeletal dysplasia in nine of nine cases. CONCLUSIONS: The femur length/abdominal circumference ratio may be useful to predict a lethal fetal outcome when ultrasonography indicates a possible skeletal dysplasia. (Am J Obstet Gynecol 1997;177:864-9.)