• Vol. 40 No. 7, 315–318
  • 15 July 2011

Second Trimester Prenatal Screening for Down’s Syndrome in Mainland Chinese Subjects using Double-Marker Analysis of α-fetoprotein and β-human Chorionic Gonadotropin Combined with Measurement of Nuchal Fold Thickness

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ABSTRACT

Introduction: This study examines the effectiveness of double-marker analysis for α-fetoprotein (AFP) and β-human chorionic gonadotropin (β-hCG) combined with measurement of nuchal fold thickness (NT) in the detection of Down’s syndrome (DS) in Mainland Chinese subjects during second trimester prenatal screening.

Materials and Methods: We examined pregnant women with a singleton pregnancy between 15 and 21 weeks of gestation who underwent second trimester screening for DS using double-marker analysis for AFP and β-hCG combined with ultrasound measurement of NT. The combined risk of DS was calculated. A cut-off of 1/270 was used to define a pregnancy at high-risk of DS. Amniocentesis was offered to all patients with high-risk pregnancies.

Results: Using double-marker analysis for AFP and β-hCG in combination with measurement of NT, the detection rate of DS increased from 66.7% to 77.8% when compared with double-marker analysis alone with similar false-positive rates (4.35%, 4.83% respectively). Using receiver operating characteristic curve (ROC) analysis, we determined that the double-marker analysis combined with measurement of NT exhibited an increased area under the curve (AUC) of 0.835 (95% CI: 0.743 to 0.927) when compared to double-marker analysis alone, which had an AUC of 0.748 (95% CI: 0.635 to 0.860). In addition, both methods were more effective than any other single test such as AFP, free β-hCG or NT measurement.

Conclusion: Second trimester prenatal screening using double-marker analysis for AFP and β-hCG combined with measurement of NT is effective for the detection of DS in Mainland Chinese pregnancies.


Down’s syndrome (DS) is the most common chromosome abnormality in mankind. Previously, patients underwent invasive prenatal diagnostic tests, such as chorionic villus sampling and amniocentesis, to detect chromosomal abnormalities. However, these invasive procedures have an intrinsic risk of foetal loss. In Mainland China, second trimester double-marker analysis remains the most common approach to assess a foetus’ risk for DS4 during the second trimester, levels of α-fetoprotein (AFP) and free β-human chorionic gonadotropin (β-hCG) are used to refine estimates of risk based on maternal age. As a routine double-marker screen, this test can identify approximately 60% of foetuses with DS, with a false-positive rate (FPR) of 3% to 5.0%. Due to the high rate of false negative results, the performance of the currently used second trimester screening methods need to be evaluated.7 The effectiveness of nuchal fold thickness (NT) as an ultrasonic screening tool for Down syndrome has been independently confirmed by 2 large prospective clinical trials.

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