The Reliability of Ultrasound Markers in Identifying Fetuses With a Life-Limiting Skeletal Dysplasia

Objective: To determine the diagnostic performance of ultrasound markers associated with life-limiting fetal skeletal dysplasia in a fortified cohort. Methods: Retrospective review from 2013 to 2023 of pregnancies with suspected fetal skeletal dysplasia. Ultrasound evaluation included measurements predictive of a life-limiting dysplasia: thoracic circumference/abdominal circumference (TC/AC) < 0.6, femur length/abdominal circumference (FL/AC) < 0.16, and thoracic circumference (TC) < 2.5th percentile. Demographics, ultrasound findings, genetic testing, and fetal/neonatal outcome were reviewed. Results: Of 96 fetuses with complete outcome data, 47 (49%) had a non-life-limiting dysplasia and 49 (51%) had a life-limiting dysplasia. 22 (23%) had no life-limiting markers, 42 (44%) had one, 27 (28%) had two, and 5 (5%) had three. FL/AC < 0.16 and TC < 2.5th percentile were associated with life-limiting dysplasia (p < 0.001; p < 0.001), while TC/AC < 0.6 was rare and did not reach statistical significance (p = 0.056). The positive predictive value (PPV) for predicting life-limiting dysplasia increased from 50% to 78% to 100% with one, two, or three markers. The PPV of the two life-limiting markers was significantly higher in those diagnosed at < versus ≥ 28 weeks (90% vs. 43%, p = 0.02) but the analysis was limited by small numbers in the ≥ 28 weeks cohort. The negative predictive value of no life-limiting markers was 91%. Conclusions: In our cohort, the presence of two life-limiting ultrasound markers prior to 28 weeks was highly suggestive of a life-limiting dysplasia, whereas the absence of life-limiting markers was strongly associated with a non-life-limiting dysplasia throughout gestation. Nonetheless, individual markers had a poor predictive value of lethality, and a life-limiting diagnosis ≥ 28 weeks is challenging based on ultrasound markers alone. This highlights the importance of integrating thorough sonography, genetic testing, and balanced parental counseling.