Debates on Down Syndrome Screening in Iran

In some countries, measurement of nuchal translucency (NT) is incorporated into national antenatal screening programmes to help detect pregnancies at increased risk of Down syndrome. Accurate measurement of the NT requires a specific technique. This article is an illustrated practical guide outlining the steps required for measuring the NT; it provides useful tips for improving operator technique and advises how to avoid common pitfalls. Although fetal nasal bone assessment does not currently form part of official Down syndrome screening programmes (in Australia or the UK), it is included here as debate about its usefulness continues.

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Hyperglycosylated Human Chorionic Gonadotropin (Invasive Trophoblast Antigen) Immunoassay: A New Basis for Gestational Down Syndrome Screening

Clinical Chemistry ◽

10.1093/clinchem/45.12.2109 ◽

1999 ◽

Vol 45 (12) ◽

pp. 2109-2119 ◽

Cited By ~ 80

Author(s):

Laurence A Cole ◽

Shohreh Shahabi ◽

Utku A Oz ◽

Ray O Bahado-Singh ◽

Maurice J Mahoney

Keyword(s):

Down Syndrome ◽

False Positive ◽

False Positive Rate ◽

Normal Karyotype ◽

Screen Test ◽

Β Subunit ◽

Second Trimester ◽

Marker Test ◽

Positive Rate ◽

Down Syndrome Screening

Abstract Background: Serum human chorionic gonadotropin (hCG) and hCG free β-subunit tests are used in combination with unconjugated estriol and α-fetoprotein in the triple screen test, and with the addition of inhibin-A in the quadruple marker test for detecting Down syndrome in the second trimester of pregnancy. These tests have a limited detection rate for Down syndrome: ∼40% for hCG or free β-subunit alone, ∼60% for the triple screen test, and ∼70% for the quadruple marker test, all at 5%, or a relatively high, false-positive rate. New tests are needed with higher detection and lower false rates. Hyperglycosylated hCG (also known as invasive trophoblast antigen or ITA) is a new test. It specifically detects a unique oligosaccharide variant of hCG associated with Down syndrome pregnancies. We evaluated this new Down syndrome-directed test in prenatal diagnosis. Methods: Hyperglycosylated hCG was measured in urine samples from women undergoing amniocentesis for advanced maternal age concerns at 14–22 weeks of gestation, 1448 with normal karyotype and 39 with Down syndrome fetuses. Results: The median hyperglycosylated hCG value was 9.5-fold higher in Down syndrome cases (9.5 multiples of the normal karyotype median). The single test detected 80% of Down syndrome cases at a 5% false-positive rate. Urine hyperglycosylated hCG was combined with urine β-core fragment (urine breakdown product of serum hCG free β-subunit), serum α-fetoprotein, and maternal age-related risk. This urine-serum combination detected 96% of Down syndrome cases at a 5% false-positive rate, 94% of cases at a 3% false-positive rate, and 71% of cases at a 1% false-positive rate. These detection rates exceed those of any previously reported combination of biochemical markers. Conclusions: Hyperglycosylated hCG is a new base marker for Down syndrome screening in the second trimester of pregnancy. The measurement of hyperglycosylated hCG can fundamentally improve the performance of Down syndrome screening protocols.

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