External Quality Assessment of Maternal Serum Levels of Alpha-Fetoprotein, Free Beta-Human Chorionic Gonadotropin, and Unconjugated Estriol in Detecting Down Syndrome and Neural Tube Defects in the Second Trimester of 87 Maternal Serum Samples, Based on 105-139 Days

BACKGROUND: We aimed to insure the accuracy and reproducibility of alpha-fetoprotein (AFP), free beta-human chorionic gonadotropin (free β-hCG), and unconjugated estriol (uE3) concentrations for the screening for trisomy 21 (T21) and neural tube defects (NTD) in the second trimester. We conducted an external quality assessment of 6 laboratories, using maternal serum specimens. MATERIAL/METHODS: Serum specimens collected from 87 women of singleton pregnancies (4 with T21, 5 with NTD, and 78 with normal fetuses) were divided into 6 equivalent-volume fractions and transported to 6 laboratories (A, B, C, D, E, and F). All laboratories used the time-resolved fluorescence analyzer and supporting reagents to measure concentrations of AFP, free β-hCG, and uE3. The screening efficacies of T21 and NTD were compared with the certified or accredited status of the participants’ quality systems. RESULTS: Concentrations of AFP measured by laboratory F were low compared with those determined by the other 5 laboratories, and the differences were significant (P<0.01). There was no statistically significant difference in the free β-hCG and uE3 concentrations measured by the 6 laboratories (P>0.05). The correlation coefficients for the 3 multiples of the median values were all >0.900. The McNemar paired chi-squared test showed the differences in the positivity and detection rates were not statistically significant (P=1.000). CONCLUSIONS: AFP, freeβ-hCG, and uE3 values measured by the other 5 laboratories were comparable with those of laboratory A, with good linear correlation. When used in the maternal prenatal screening of T21 and NTD, the test results met the clinical requirements.