Background: First trimester prenatal screening gives the risk rates associated with aneuploidies. Measurement uncertainty is defined as a magnitude showing distribution of the measured values. The aim of this study is to investigate the effects of measurement uncertainty on prenatal screening and compare two different measurement uncertainty guidelines which suggest different equations.

Material and Methods: This retrospective study was performed with results of 544 patients. Uncertainties of free-βsubunit human Chorionic Gonadotropin (free β-hCG) and Pregnancy Associated Protein-A (PAPP-A) were calculated as defined by AACB and Nordtest guides.The best-case and the worst-case scenarios were created for risk rates of trisomies. New risks were recalculated by adding and subtracting uncertainty values from free β-hCG and PAPP-A.

Results: The number of patients who have a risk rate >1:1500 and to be subject to further investigation was 58. This number decreased to 38 and 36 with best-case scenarios, while the number increased to 94 and 99 with worst-case scenarios with the uncertainty values obtained from the AACB and Nordtest guidelines, respectively (P<0.005). There was a significant difference between median risks of the patients with two guidelines with best-case and the worst-case scenarios(P<0.005).

Conclusions: When a result is calculated with multiple parameters, calculation of uncertainty and reporting with the result may significantly affect the outcome. The measurement uncertainty equation to be selected is also important.