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NHS Fetal Anomaly Screening Programme (including chromosomal disorders)

NHS England Screening NHS Fetal Anomaly Screening Programme (FASP) NICE guideline [NG201] Antenatal care. Aug 2021.

Guidelines

There are 2 main screening pathways:
  • Combined test and/or quadruple test - for trisomy 21, 18, 13
  • 20 week screening scan (anomaly scan) - for 11 physical conditions
    • Offered 18+0 - 20+6 weeks

Approach
  • Firstly screen with combined and/or quadruple test (these test simply gives a result of higher or lower chance)
  • If higher chance → 2nd line tests 
 

Test of choice: the combined test, performed between 10-14 weeks

2nd line: quadruple test performed between 14-20 weeks. Indications:
  • Women attends antenatal care after 14 weeks 
  • If not eligible for combined test or unable to measure NT (see below for more details)

If combined test and/or quadruple test gives a result of  higher chance → proceed to definitive testing (prenatal diagnosis)
 

The combined test is able to screen for trisomy 21, 18, 13 (Down's, Edward's, Patau's syndrome)

The combined test involves assessing:
  • Maternal age
  • Biochemical marker - free bhCGbeta human chorionic gonadotropin and PAPP-APregnancy associated plasma protein-A
  • Nuchal translucency

Result trend that is suggestive of Down's syndrome:
  • ↑ b-HCG
  • ↓ PAPP-A
  • ↑ Nuchal translucency (≥3.5 mm)

Note that the quadruple test only assess the chance of the baby having trisomy 21 (Down's syndrome).

The quadruple test involves assessing 4 biochemical markers:
  • b-HCG
  • Inhibin-A
  • AFP
  • Unconjugated oestriol 

Results trend that is suggestive of Down's syndrome
  • ↑ b-HCG
  • ↑ Inhibin-A
  • ↓ AFP
  • ↓ Unconjugated oestriol 

Disclaimer: eligibility criteria for combined test and quadruple test has been omitted above due to its advanced level of knowledge which may create confusion.

Eligibility criteria for combined test:

  • CRL 45 - 84 mm
    • If CRL <45 mm → recall for a further US
    • If CRL >84 mm → calculate gestational age using HC and offer quadruple test if criteria met
Eligibility criteria for quadruple test:
  • NT measurement cannot be obtained
  • CRL >84 mm
  • HC 101 - 172 mm
    • If HC >172 mm → offer 20 week screening scan (anomaly scan)

For higher chacne result, offer the women a choice of:
  • NIPT, or
  • CVS or amniocentesis (confirmatory tests)
 

Timing: ≤ 21+6 weeks (first sample)

Involves a maternal blood test to analyse cffDNA that circulate in the maternal circulation.

NIPT results are reported as lower chance / higher chance:
  • If higher chance → offer the option of no fruterh testing for PND
 

Note that NIPT is still a screening test, that is more accurate than the combined and quadruple test. Yet, it is not a diagnostic test, unlike chorionic villus sampling or amniocentesis. 

These are the only confirmatory test for prenatal diagnosis of T21, 18, 13.

Chorionic Villus Sampling:
  • Timing: 11-14 weeks 
  • Description: ultrasound guided transabdominal / transcervical procedure to obtain a sample of placental tissue for chromosomal or genetic analysis

Amniocentesis:
  • Timing: 15-20 weeks
  • Description: ultrasound guided extraction of amniotic fluid for chromosomal or genetic analysis 
 

NHS England: One in 200 women who have a  CVS or amniocentesis will miscarry.

The 20 week screening scan is also known as the anomaly scan:
  • Timing: 18+0 - 20+6 weeks 
  • Description: ultrasound scan to screen for 11 physical conditions

If scan detected / raised suspicion of physical conditions:
  • Refer 
  • Offer confirmatory testing (chorionic villus sampling or amniocentesis)
  • Discuss options of continue pregnancy vs terminate pregnancy 
 

  • Trisomy 18 and 13 (Edward's and Patau's syndrome)
  • 2 neural tube defect (anencephaly and spina bifida)
  • 3 GI defect (cleft lip, gastroschisis, exomphalos)
  • Congenital diaphragmatic hernia
  • Congenital heart disease
  • Bilateral renal agenesis
  • Severe skeletal dysplasia

References

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Author: Adams Lau
Reviewer: 
Last Edited: 07/03/25