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

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Key messages from the NHS Fetal Anomaly Screening Programme:

• All pregnant women should be offered screening for Down's syndrome.
• Women should understand that it is their choice to embark on screening for Down's syndrome.
• 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.
• Tests should meet a detection rate (DR) of more than 75%, for a screen positive rate (SPR) of less than 3% (of affected pregnancies) for England for those undergoing quadruple screening.
• Screening for Down's syndrome can be undertaken from 10 weeks + 0 days to 20 weeks + 0 days of pregnancy.
• 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.
• The overall timeline for pregnancy chromosomal screening (test) and the laboratory risk calculation is from 10 weeks + 0 days to 20 weeks + 0 days of pregnancy.
• When it is not possible to measure nuchal translucency as part of combined screening, owing to fetal position or raised body mass index, women should be offered the quadruple test.
• 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.
  • 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.
• GP's should receive an annual report of local screening programmes
  
  
• www.screening.nhs.uk/fetalanomaly

Information about screening for Down's syndrome should be given to pregnant women at the first contact with a healthcare professional. This will provide the opportunity for further discussion before embarking on screening. Specific information should include:

• the nature of the screening test offered locally, how it is done, and timing of the test;
• the possible meaning and implication of the test results as well as potential significant clinical and emotional consequences;
• the decisions that might need to be made at each point along the pathway and their consequences;
• how and when the results will be given;
• the screening pathway for Down's syndrome screening, including how the pathway might change for those with both lower risk and higher risk Down's syndrome screening results, and for women who do not opt to have screening;
• the screening pathway for fetal anomaly screening, including those women who do not opt to have screening;
• the possibility that screening can provide information about other conditions;
• the fact that screening does not provide a definitive diagnosis;
• information about chorionic villus sampling and amniocentesis;
• that confirmatory/repeat testing may occasionally be required;
• balanced and accurate information about the various conditions being screened for;
• balanced and accurate information about Down's syndrome.
  
  
• if a pregnant woman receives a screen-positive result for Down's syndrome, she should have rapid access to appropriate counselling by trained staff.
• routine anomaly scan (at 18 weeks 0 days to 20 weeks 6 days) should not be routinely used for Down's syndrome screening using soft markers.
• the presence two or more isolated soft marker, with the exception of increased nuchal fold, on the routine anomaly scan, should not be used to adjust the a priori risk for Down's syndrome.
• the presence of an increased nuchal fold (6 millimetres or above) or two or more soft markers on the routine anomaly scan should prompt the offer of a referral to a fetal medicine specialist or an appropriate healthcare professional with a special interest in fetal medicine

The Fetal Anomaly screening programme has working groups looking at standards, and education and training. Further information on all above aspects is available here: www.fetalanomaly.screening.nhs.uk

Note that NICE states (1) a different timeline for combined and quadruple tests (1):

• the 'combined test' (nuchal translucency, beta-human chorionic gonadotrophin, pregnancy-associated plasma protein-A) should be offered to screen for Down's syndrome between 11 weeks 0 days and 13 weeks 6 days. For women who book later in pregnancy the most clinically and cost-effective serum screening test (triple or quadruple test) should be offered between 15 weeks 0 days and 20 weeks 0 days

Reference:

1. NICE (March 2016). Antenatal care for uncomplicated pregnancies
2. NHS Fetal Anomaly Screening Programme. Antenatal screening - working standards for Down's syndrome screening 2007. NHS FASP; 2007.
3. NHS Fetal Anomaly Screening Programme. Consent standards for screening fetal anomalies during pregnancy 2007. NHS FASP; 2007.
4. 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.
5. 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.