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Combined test in Down's screening

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Ultrasound screening in Down's syndrome

  • there have been significant developments in using ultrasound techniques as a screening tool for Down's syndrome
    • during the first trimester in the majority of pregnancies, it is possible to measure the size of the fluid area at the back of the fetus's neck, known as the nuchal translucency or NT. The increasing size of the NT indicates a greater risk of the fetus having Down's syndrome
    • both biochemical and ultrasound screening methods can be combined to give a better detection rate. This is the suggested way forward for screening in England is the Combined Test in the first trimester.
    • NT is the only ultrasound marker that should be used. Measurement of other markers, including the nasal bone, should be done only in the context of an ethically approved research project

      • Screening for Down's syndrome can be undertaken from 10 weeks + 0 days to 20 weeks + 0 days of pregnancy. The recommended method of screening for Down's syndrome is using the Combined Test
      • Screening for Down's syndrome should be performed by the end of the first trimester (14 weeks and 1 day), but provision should be made to allow later screening (which could be as late as 20 weeks 0 days) for women booking later in pregnancy
      • Tests should meet a detection rate (DR) of more than 90%, for a screen positive rate (SPR) of less than 2% (of affected pregnancies) for England for those undergoing combined screening
      • The following tests meet current standards:
        • From 10 weeks + 0 days to 14 weeks + 1 day the combined test (maternal serum - hCG and PAPP-A and nuchal translucency scan) is the recommended screening strategy
          • the blood sample (or serum sample) can be taken between 10 weeks and 0 days and 14 weeks and 1 day's gestation. The blood sample uses a combination of free beta-hCG and placenta associated plasma protein A (PAPP-A)
          • the NT and CRL measurement can be taken between 11 weeks and 2 days and 14 weeks and 1 days gestation
        • From 14 weeks + 2 days to 20 weeks + 0 days, the quadruple test (maternal serum - hCG, AFP, uE3, inhibin A)) for those presenting later is the recommended screening strategy

For more information:

Down's screening programme (part of the Fetal Anomaly Screening Programme)

Reference:

  • NICE. Antenatal care: routine care for the healthy pregnant woman. England: NHS National Institute for Health and Clinical Excellence; 2008 Mar. Report No.: Clinical guidelines CG62.
  • NHS Fetal Anomaly Screening Programme. Antenatal screening - working standards for Down's syndrome screening 2007. NHS FASP; 2007.
  • NHS Fetal Anomaly Screening Programme. Consent standards for screening fetal anomalies during pregnancy 2007. NHS FASP; 2007.
  • NHS Fetal Anomaly Screening Programme. NHS fetal Anomaly screening programme - screening for Down's syndrome: UK NSC Policy recommendations 2007-2010: Model of Best Practice. Department of Health; 2008.
  • Kirwan D, NHS FASP. 18+0 to 20+6 weeks fetal anomaly scan -National standards and guidance for England 2010. Exeter, England: NHS Fetal Anomaly Screening Programme; 2010.

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