2083179 Algorithm for Skeletal Dysplasias by Prenatal Ultrasound: Emphasis on Predicting Lethality

We describe a simplified algorithm for determining lethality of a suspected skeletal dysplasia by prenatal ultrasound. Goals Understand when to consider the diagnosis of a skeletal dysplasia Recognize accurate predictors that constitute a lethal skeletal dysplasia Recognize sonographic features of the major lethal skeletal dysplasias and the unique features that distinguish one from another A literature review of all predictors of lethality in skeletal dysplasias was performed. The most reliable predictors of lethality were determined using relative sensitivity, specificity, negative predictive value, and positive predictive value. We combined the most reliable predictors of lethality to create an original, logical, and simple algorithm to accurately determine those skeletal dysplasias that are incompatible with life. A diagnosis of skeletal dysplasia should be considered based on early, severe shortening of all the long bones (at least 2-3 standard deviations below the mean) with inability to maintain growth along a growth curve. With the exception of chondrodysplasia punctata, only the micromelic forms of skeletal dysplasias are lethal. The most reliable predictor of lethality among the micromelic forms, which contains both lethal and variable prognosis dysplasias, is the femur length-to-abdominal circumference ratio. A ratio < 0.16 is highly predictive of a lethal skeletal dysplasia. Other reliable predictors of lethality include the chest circumference-to-abdominal circumference ratio < 0.6, the presence of bowing and/or fractures, decreased bone mineralization, and an abnormal number of bones. Although a specific prenatal diagnosis of the exact type of skeletal dysplasia is only made in little over half of all cases, lethal cases can be determined with nearly 100% accuracy, using a relatively simple diagnostic algorithm. Accurate prenatal identification of lethal dysplasias allows for early parental counseling and possible pregnancy termination as well as genetic assessment prior to future pregnancy.