Lung Hypoplasia in Fetuses with Skeletal Dysplasia Determined by Fetal Lung Weight: Which Ultrasound Measurement/Ratio Has the Highest Detection Rate

Introduction: To determine lung hypoplasia in cases with fetal skeletal dysplasia based on the total lung weight at autopsy as the most accountable surrogate marker for pulmonary hypoplasia.

Methods: This retrospective cohort study included all pregnancies with antenatal diagnosis of skeletal dysplasia (2012-2018). We included only cases in which information on fetal biometry was available within 2 weeks before delivery and had autopsy and skeletal X-rays + molecular analysis using extracted fetal DNA. We compared the predictive accuracy of fetal sonographic body-proportional ratios (BPRs) including: (1) thoracic circumference-to-abdominal circumference ratio, (2) the femur length-to-abdominal circumference (FL/AC) ratio, (3) head circumference-to-abdominal circumference ratio, and (4) foot length-to-femur length ratio. Lung hypoplasia was defined as total lung weight below -2 SD from the expected mean for gestational age.

Results: Fifty three pregnancies with antenatal diagnosis of skeletal dysplasia underwent autopsy included. Lung hypoplasia was determined in 34 (64.1%). Median of gestational age at last sonographic assessment was 21.3 (19.9-24.9) weeks. FL/AC ratio demonstrated the highest area under the curve of 0.817 (95% CI: 0.685-0.949; p < 0.0001). FL/AC ≤0.1550 demonstrated the highest detection rate of 88.2% along with the highest negative predictive value of 75%.

Conclusion: Using a novel, more practical approach to predict lung hypoplasia in skeletal dysplasia, fetal sonographic BPRs and, specifically, FL/AC ratio demonstrate a high detection rate of lung hypoplasia.