Prenatal diagnosis of fetal skeletal dysplasias in a tertiary Hospital in Spain.

Objective: To assess the diagnostic accuracy of prenatal ultrasound for detecting fetal skeletal dysplasias and to describe its role in orienting genetic studies.

Study Design: Observational study of pregnant women surveyed in our hospital, between 2011 and 2018, with fetal long bones below the 3rd centile (shortened long bones), either as an isolated finding or associated to other skeletal anomalies. We used a systematic protocol for the ultrasound evaluation and selection of those fetuses suspected of having a skeletal dysplasia. We report the demographics of these patients along with the sonographic follow-up of their fetuses, the genetic results and the outcome of the pregnancies and the newborn in the entire group and also compare data between the two sub-groups (isolated shortened long bones vs shortened long bones associated to other anomalies).

Results: A total of 81 pregnancies with a suspected fetal skeletal dysplasia were included, with a complete follow-up available in 75 cases, 22 with isolated shortened long bones and 53 cases that presented shortened long bones with other skeletal anomalies. In the shortened long bones sub-group, a total of five (23 %) were born healthy neonates, 10 (45 %) were small for gestational age or intrauterine growth restricted (one of them of genetic origin) and seven (32 %) had a skeletal dysplasia (6 of them with genetic diagnosis). Whilst among the 53 cases that presented with shortened long bones + other skeletal anomalies, three (6%) were healthy neonates, five (9%) were small for gestational age/intrauterine growth restricted (two of genetic origin) and 45 (85 %) had a skeletal dysplasia (19 genetically confirmed and 26 with a clinical diagnosis). These differences in frequencies between the two sub-groups were determined to be statistically significant (χ: p = 0.02).

Conclusion: Around one third of fetuses with isolated shortened long bones will have a skeletal dysplasia. If abnormal skeletal ultrasound findings are associated with shortened long bones, the risk for skeletal dysplasia is significantly increased (85 %). Prenatal systematic approach in a multidisciplinary unit is useful in the orientation of genetic studies.