All women who book for care prior to 19 completed weeks of gestation are screened for anomalies.
1st trimester screening (combined test)
Performed from 11+2 to 14+1 for singleton and twin pregnancies, this test involves a Nuchal translucency scan and a maternal blood test.
Following discussion with their community midwife and being given written information* to consider, women have the following options:
- No screening for aneuploidy
- Screening for T21 (Down's Syndrome) only
- Screening for T18 and T13 (Edwards' and Patau Syndromes) only
- Screening for all 3 conditions T21, T18, T13 (Down's, Edwards' and Patau Syndromes)
*Translations, information in Braile and simplified pictorial format versions are available
2nd trimester (Quadruple test) screening
For women booking for care after 14+2 or for whom Nuchal translucency measurements are not possible.
This test can be carried out until 19+6 and involves measuring maternal blood markers AFP, Oestriol, HcG and Inhibin A for singleton and Twin pregnancies (see additional pathway for serum screening in twin pregnancies) and screens only for T21 (Down's Syndrome).
The main aim of the NHS screening programme for fetal anomaly ultrasound is to offer all pregnant women in England a minimum of two ultrasound scans.
The first is an early scan, undertaken after eight weeks gestation and used mainly for dating the pregnancy and confirming viability.
The second ultrasound scan is undertaken between 18+0 to 20+6 weeks of pregnancy and screens for major structural anomalies.
Diagnostic testing: pre-natal diagnosis (PND)
Following fetal anomaly or a high risk screening result, women will have the opportunity to discuss implications of the findings and options for further testing within 24 hours.
- Consent is obtained and the woman's decision is documented in the health care records
- The woman is given information on how the results of PND may be communicated to her and a method agreed
- PND is performed in accordance with RCOG and NICE Guidelines. Note: PND for a Multiple Pregnancy should be conducted at a tertiary Fetal Medicine Unit due to the specialised nature of the procedures and the increased risk of miscarriage.
- A sample is obtained by chorionic villus sampling (CVS) (between 10+0 and 13+6 weeks) or amniocentesis (after 15+0 weeks)
- Where the indication for undertaking PND is a higher risk screening result, the sample is sent to the cytogenetic laboratory for quantitative fluorescence polymerase chain reaction (QF-PCR) testing
- Local protocols should be in place between the laboratory and maternity service to log receipt of a fit for purpose sample, deal with incomplete information on the request form, or any unacceptable samples that require repeat specimens. This should be done as soon as practicable to ensure timely processing of samples and all requests should be tracked until completed
- Following referral for diagnostic testing, information should be shared between the specialist teams, maternity services and primary care to ensure appropriate pregnancy management/delivery of the baby and monitoring of screening outcomes
- Local protocols should be in place to ensure multi-disciplinary links and close working relationships between maternity services and specialist services are established
Management of diagnostic test results
- The woman is given the opportunity to discuss the results with health professionals who are knowledgeable about Down's, Edwards' and Patau Syndromes. This will include the offer of a termination of pregnancy or continuing support through pregnancy
- If the woman chooses not to undergo termination of pregnancy and continues with her pregnancy a referral to appropriate paediatric and support services should be made
- A pregnancy outcome should be recorded and a mechanism should be in place to alert the practitioners providing subsequent care (including the newborn physical examination)
- If termination of pregnancy is accepted, this should be undertaken in line with the Abortion Act 1967
A local protocol should be in place for reporting and appropriate referral of any babies born with suspected/confirmed Down's, Edwards' and Patau Syndromes who were not identified in the antenatal period, to allow review of the woman's participation in the screening pathway.