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First Trimester Screen, Hyperglycosylated hCG (h-hCG)

First Trimester Screen, Hyperglycosylated hCG (h-hCG)

Test Summary

First Trimester Screen, Hyperglycosylated hCG (h-hCG)

  

Clinical Use

  • Prenatal (first trimester) risk assessment for Down syndrome and trisomy 18

Clinical Background

Prenatal testing for Down syndrome and trisomy 18 risk assessment is routinely offered to pregnant women in the second trimester of pregnancy. First-trimester screening, however, is advantageous in that 1) positive results can lead to earlier diagnosis and 2) when pregnancy termination is elected, there is more privacy and reduced maternal morbidity. The first trimester screen detection rate, at a constant false-positive rate, is higher than that of the triple screen and the same as that of the quad screen performed in the second trimester.1 The American College of Obstetricians and Gynecologists (ACOG) thus considers first-trimester screening a reasonable option.1

This first-trimester maternal serum screening test includes maternal age, pregnancy-associated plasma protein-A (PAPP-A), hyperglycosylated hCG (h-hCG), and nuchal translucency (NT). PAPP-A is a placental protein generally present in lower concentrations in Down syndrome-affected pregnancies relative to unaffected pregnancies. h-hCG is a hyperglycosylated form of human chorionic gonadotropin (hCG) that is produced by cytotrophoblasts during embryonic implantation and trophoblast invasion of the uterine wall. Levels tend to be increased in Down syndrome-affected pregnancies. NT is an ultrasonographic measurement of a fluid-filled space at the back of the fetal neck. NT tends to be elevated in cases of fetal aneuploidy (eg, Down syndrome). Palomaki and colleagues showed that this screening test is equivalent to the PAPP-A, free-β hCG, and NT combination for Down syndrome screening (see Table).2,3

Table. Down Syndrome Detection Rates (DRs)2
DR, %
Age, PAPP-A, h-hCG, NT 84

Age, PAPP-A, free-β hCG, NT

84
 
Age, PAPP-A, h-hCG 67
Age, PAPP-A, free-β hCG 67
a At a 5% false-positive rate.

Individuals Suitable for Testing

  • Women in their first trimester of pregnancy

Method

  • PAPP-A: enzyme immunoassay (EIA)

  • h-hCG: electrochemiluminescence assay

  • The multiple of the median (MoM) is calculated for PAPP-A, h-hCG, and NT.

  • PAPP-A and h-hCG MoM values are adjusted for maternal weight.

  • Down syndrome risk is based on all 3 MoM values, combined with the maternal age at time of delivery. Expected detection rate is 84% at a 5% false-positive rate.2

  • Trisomy 18 risk is based on maternal age, PAPP-A, and NT. Expected detection rate is 75% at a 0.5% false-positive rate.4

  • If the NT measurement is not provided, the Down syndrome risk will be based on age, PAPP-A, and h-hCG, and the trisomy 18 risk will be based on age and PAPP-A.

  • Neural tube defect (NTD) risk is not provided. For NTD risk, order a second-trimester (16-18 weeks’ gestation) AFP test.

  • Aliases: Maternal Serum Screen, 1st Trimester; invasive trophoblast antigen (ITA, h-hCG)

Interpretive Information

Women with a risk <1:270 (Down syndrome) or <1:100 (trisomy 18) are considered at low risk of carrying an affected fetus. Since this is a screening test, such risks cannot guarantee the birth of an unaffected baby.

Women with a risk ≥1:270 (Down syndrome) or ≥1:100 (trisomy 18) are considered at increased risk of carrying an affected fetus. Genetic counseling and possible diagnostic testing are recommended.

Inaccurate gestational age and NT measurements can substantially impact risk assessment. Ultrasound confirmation of gestational age is strongly suggested. Risks can be recalculated if necessary; call 1-866-GENE-INFO (1-866-436-3463).

References

  1. ACOG Practice Bulletin No. 77: screening for fetal chromosomal abnormalities. Obstet Gynecol. 2007;109:217-227.

  2. Palomaki GE, Knight GJ, Neveux LM, et al. Maternal serum invasive trophoblast antigen and first-trimester Down syndrome screening. Clin Chem. 2005;51:1499-1504.a

  3. Palomaki GE, Neveux LM, Haddow JE, et al. Hyperglycosolated-hCG (h-hCG) and Down syndrome screening in the first and second trimesters of pregnancy. Prenat Diagn. 2007;27:808-813.a

  4. Tul N, Spencer K, Noble P, et al. Screening for trisomy 18 by fetal nuchal translucency and maternal serum free β-hCG and PAPP-A at 10-14 weeks of gestation. Prenat Diagn. 1999;19:1035-1042.

Related References

  1. Weinans MJN, Sancken U, Pandian R, et al. Invasive trophoblast antigen (hyperglycosylated hCG) as a first-trimester serum marker for Down�s syndrome. In: Weinans M, ed. Operationalization of First Trimester Maternal Serum Screening for Down�s Syndrome. Wageningen: Ponsen & Looyen BV; 2004:111-122.a

  2. Wald NJ, Rodeck C, Hackshaw AK, et al. First and second trimester antenatal screening for Down’s syndrome: the results of the Serum, Urine and Ultrasound Screening Study (SURUSS). J Med Screen. 2003;10:56-104.

  3. Palomaki GE, Knight GJ, Robertson MM, et al. Invasive trophoblastic antigen (hyperglycosylated human chorionic gonadotropin) in second-trimester maternal urine as a marker for Down syndrome: preliminary results of an observational study on fresh samples. Clin Chem. 2004;50:182-189.

  4. Weinans MJ, Butler SA, Mantingh A, Cole LA. Urinary hyperglycosylated hCG in first trimester screening for chromosomal abnormalities. Prenat Diagn. 2000;20:976-978.

  5. Cuckle HS, Shahabi S, Sehmi IK, et al. Maternal urine hyperglycosylated hCG in pregnancies with Down syndrome. Prenat Diagn. 1999;19:918-920.

  6. Cole LA, Shahabi S, Oz UA, et al. Urinary screening tests for fetal Down syndrome: II. Hyperglycosylated hCG. Prenat Diagn. 1999;19:351-359.

  7. Cole LA, Omrani A, Cermik D, et al. Hyperglycosylated hCG, a potential alternative to hCG in Down syndrome screening. Prenat Diagn. 1998;18:926-933.
     

a This study was funded in part by Quest Diagnostics; however, Quest Diagnostics did not participate in the data analysis or influence the conclusions reached by the authors.

This test is performed using a kit that has not been approved or cleared by the FDA. The analytical performance characteristics of this test have been determined by Quest Diagnostics Nichols Institute. This test should not be used for diagnosis without confirmation by other medically established means.
Content reviewed 12/2011
 
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