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First Trimester Screen, hCG

First Trimester Screen, Hyperglycosylated hCG (h-hCG)

Test codes: 16020, 16145, 16968[NY], 16969[NY]

A negative screen means it is unlikely the fetus has Down syndrome or trisomy 18. 

The first-trimester screening test screens only for Down syndrome and trisomy 18. American College of Obstetricians and gynecologists (ACOG) recommends neural tube defect screening be performed in the second trimester.1 The Maternal Serum AFP test (test code 5059 or 92788[NY]) is available for this purpose.

A positive screening result for Down syndrome means there is an increased risk for the fetus to be affected with Down syndrome or other chromosome abnormalities.

The American College of Obstetricians and Gynecologists (ACOG) recommends that women with a positive screening test receive counseling to discuss the significance of the screening results and diagnostic testing options such as chorionic villus testing or amniocentesis.1

The earliest ultrasound-derived EDD should be used for dating purposes.2 For patients who screen positive for Down syndrome, EDD can be updated if appropriate and risk can be recalculated. An ultrasound-derived EDD is most accurate when determined in the first trimester. If a first-trimester ultrasound EDD is available and is within ±7 days of the gestational age used for the screening test, the gestational age should not be changed for screening purposes.

If a second-trimester (but not first-trimester) EDD is available and the gestational age is  ±10 days of the EDD used for screening, the gestational age should not be changed for screening purposes. If the gestational age used for screening is outside the ultrasound EDD range, it may be appropriate to change the gestational age used for screening.2 Please call Quest Genomics Clients Services at 1.866.GENE.INFO (1.866.436.3463) to change EDD.

Please call Quest Genomics Client Services at 1.866.GENE.INFO (1.866.436.3463) to talk to a genomic science specialist. Documentation of the abnormality in the family may enable a more specific risk assessment or indicate whether additional studies should be performed. 

A cutoff of 1 in 270, the risk of a 35-year old, is used to determine if a pregnancy is screen negative or screen positive for Down syndrome. This cutoff is used regardless of the patient’s age because it is the historical cutoff for offering diagnostic testing (amniocentesis).

When counseling a pregnant patient, it may be helpful to compare her age-related risk (ie, pre-test risk) with her screen-derived risk (post-test risk) and the general population risk (1 in 600-800 live births). This allows the patient and her partner to better understand her risk of carrying a Down syndrome-affected fetus and to weigh it against the risks and consequences of amniocentesis. 

The serum markers can be measured in a patient with a twin gestation and then divided by corresponding medians for unaffected singleton pregnancies to calculate multiple-of-medians (MoMs). This measurement undergoes an adjustment that accounts for the presence of 2 fetuses, and also takes into account the nuchal translucency measurement of each specific fetus. The result is a pregnancy-specific pseudo-risk, rather than a fetus-specific risk.

A trisomy 18 risk assessment is not calculated for twin gestations due to insufficient screening marker data from affected twin pregnancies.

References

  1. ACOG Committee on Practice Bulletins. ACOG Practice Bulletin No. 226: screening for fetal chromosomal abnormalities. Obstet Gynecol. 2020;136(4):1-22.
  2. American College of Obstetricians and Gynecology. Committee Opinion No 700: Method for estimating due date. Obstet Gynecol. 2017;129(5):e150-154.

 


This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on the physician’s education, clinical expertise, and assessment of the patient.


Document FAQS.82 Version: 4

Version 4 effective 12/01/2023 to present

Version 3 effective 01/12/2016 to 12/01/2023
Version 2 effective 09/23/2014 to 01/11/2016
Version 1 effective 04/24/2013 to 09/22/2014
Version 0 effective 10/15/2012 to 04/23/2013