Objective: To assess the interobserver variability of ultrasound measured fetal nuchal thickness (NT).
Study design: NT was measured in 103 consecutive early midtrimester pregnancies (13-18 weeks) by three ultrasonographists with different levels of expertise, in our Prenatal Unit. Measurements were obtained prior to amniocentesis, blindly in relation to other examiners' values. The Lin's concordance correlation coefficient and the Kappa statistics were used to assess concordance between observed values.
Results: Mean differences between pairs of observers ranged from 0.44 to 0.57 mm. A higher concordance correlation between measurements was obtained between the more experienced observers (r = 0.77 versus r = 0.51). When assigning cases with a NT > or = 5 mm to a group at risk for Down's syndrome, a high concordance between experienced ultrasonographists was observed (98% agreement; kappa = 0.90).
Conclusions: Interobserver variability in NT was acceptable between experienced ultrasonographists.