This screening follows the guidelines from the National Screening Committee Down’s syndrome screening programme and the 2008 NICE guidelines for Down’s syndrome screening.
The current overall standard is to meet a detection rate of more than 75% for a screen positive rate of 3% or less. By 2010, the aim is to achieve a detection rate of 90% with a screen positive rate of less than 2%.
The tests offered will depend on local availability and when a woman books for antenatal care:
Combined test
The combined test involves a blood sample for free beta hCG and PAPP-A combined with a nuchal translucency (NT) measurement between 11 weeks and 13 weeks + 6 days gestation.
Serum screening
Serum screening is offered between 15 and 20 weeks if the woman has not presented for antenatal care in time to be offered the combined test.
Once a screening test has been performed, the chance of the fetus having Down’s syndrome is calculated using software that takes into account maternal age, gestation, maternal weight, smoking and ethnicity. The woman is given a higher chance result if the probability is equal or greater than the nationally agreed cut-off level.
In the UK the current level is 1 in 50 for the combined test and 1 in 200 for serum screening.
Women receiving a higher chance result will be offered a diagnostic test; either CVS following the combined test, or amniocentesis after 15 weeks gestation.
Down’s syndrome
Details of what is offered at each obstetric unit in the country can be found at:
NHS Fetal Anomaly Screening ProgrammeNICE Guidelines – Antenatal care: routine care for the healthy pregnant woman
