First Trimester Down's Screening, Combined Test (PAPPA FBHCG) Trisomy 13 and Trisomy 18 Risk Factors

Immunology

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Description

First trimester Down's screening is carried out using the combined test which is the Foetal Anomaly Screening Programme ( FASP ) recommended protocol. The combined test measures PAPPA and free beta HCG ( FB HCG ) in the maternal serum between 11+2 and 14+1 weeks gestation. The FASP model of best practice recommends that the quadruple test ( FB HCG/Total HCG, AFP, Inhibin A and UE3 ) is performed on women who are booked in for Down's screening after 14+1 weeks [1]. A Down's risk factor is calculated by modifying the maternal age alone risk with the biochemistry results and the nuchal translucency measurement. It has been shown that the detection rate of foetuses with Down's syndrome is better when performed at 11 weeks. The calculation of trisomy 13 and trisomy 18 risk factors can also be calculated using the first trimester screening sample.

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Indications

Prenatal Down's Screening.

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Sample Type

2mL Serum ( Gel 5mL Yellow tube ). Requests from outside Sheffield: Transport at ambient temperature via Royal Mail or Courier.

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Reference Range

High risk cut off 1:150 Low risk less than 1:150. Cut off defined by FASP.

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Turnaround Time

Within 3 days

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Testing Frequency

Daily

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External Notes

Must include: weight; smoking status; ethnicity; number of foetuses; NT; CRL measurement; sonographer ID.

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References

FASP UKNSC policy Recommendations 2007-2010: Model of Best Practice. 2008. [Ref 1].
NICE Clinical Guideline 6. Antenatal Care. 2008.
Wald NJ et al. First and second trimester antenatal screening for Down's syndrome: the results of the SURUSS. HTA. 2003. 7:11.
Crossley JA, et al. Combined ultrasound and biochemical screening for Down's syndrome in the first trimester: a Scottish multicentre study. BJOG. 2002. 109:667-676.
NHS Fetal Anomaly Screening Programme Handbook 2018. Public Health England. Published August 2018.

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.