The impact of implementing non-invasive prenatal testing (NIPT) into the Scottish antenatal screening programme for Down's syndrome

Down's syndrome is a condition where an individual has three full or partial copies of chromosome 21, otherwise known as trisomy 21. There are approximately 47,000 individuals living with Down's syndrome in the UK according to the Down's Syndrome Association (DSA).

Every child with Down's syndrome is unique, following the same developmental path as all children. Most individuals with Down's syndrome will have some form of learning impairment, and some will have more complex needs, although everyone is different.

Many people with Down's syndrome lead happy and fulfilled lives, living as independently as possible and pursuing activities and occupations into their 60s, 70s and beyond. More information and insight into the lives of people with Down's syndrome can be found through the following websites:

• Down's Syndrome Association (DSA)
• NHS Inform
• Down's Syndrome Scotland

Non-invasive prenatal testing was introduced to the Scottish antenatal screening programme in September 2020.

Before September 2020

Routine screening was available for Down's syndrome only and was offered to all women with a singleton pregnancy. Women that opted for screening tests were given a chance score for the baby having Down's syndrome. This score was based on a combination of maternal blood samples and ultrasound measurements, depending on the gestation of pregnancy. Down's syndrome screening for twin pregnancies was only offered in the first trimester.

If a pregnancy was given a higher chance of Down's syndrome (i.e. >= 1 in 150), the mother was offered an invasive test to confirm the condition. These diagnostic tests (amniocentesis or chorionic villus sampling) have, however, a small risk of miscarriage.

At each stage, women could decide not to have any further testing.

This screening pathway for Down's syndrome is represented in Figure 1.

Figure 1: Flow diagram to represent the screening options for Down's syndrome for a singleton pregnancy before September 2020.

Since September 2020

All pregnant women booking for antenatal care are now offered screening for Down's, Edwards' and Patau's syndromes if they are in their first three months of pregnancy. Women that opt for screening tests, are given a chance score for the baby having either Down's syndrome or, separately, either Edwards' or Patau's syndrome, based on the same testing as before (now referred to as first line screening). Screening has also been extended to twin pregnancies in the first and second trimester for Down's syndrome.

If the chance of the baby having a specific condition is higher, women are offered another screening test called non-invasive prenatal test (NIPT), for which women only need to give a blood sample and will be told whether there is a high or low chance that the baby has the condition.

NIPT is a more accurate screening test for these three conditions, and it will hopefully reduce the need for pregnant women to undergo invasive tests. However, women can still choose to do an invasive test instead, or no further screening tests (Figure 2).

If the NIPT result is positive, women are then offered invasive testing, or no further testing.

Figure 2: Screening options available for singleton pregnancies for Down's syndrome following the September 2020 implementation of NIPT. First line screening test refers to the combined or quadruple screening available before NIPT was introduced.

Non-invasive prenatal testing (NIPT) is a screening test that analyses genetic material released from the placenta, called cell-free DNA (cfDNA). cfDNA circulates in the maternal blood stream during pregnancy and can be used for NIPT from 11 weeks gestation.

When used as a screening test, NIPT has been found to have over 99% accuracy for Down's syndrome (Taylor-Philips et al., 2016), meaning it is much more accurate than the first line screening tests. However, this is still a screening test, and there is a very small chance of being incorrect. Therefore, NIPT is not enough to diagnose a baby with Down's syndrome. To get a definitive answer for whether a baby has Down's syndrome before birth, invasive testing such as amniocentesis or chorionic villus sampling, must still be used.

For further information on NIPT please visit the NHS inform website .

Project specific:

• Chief Medical Officer letter of NIPT implementation for Scotland in 2020
• Systematic review protocol: PROSPERO protocol

Further information and resources in this field:

• NHS inform website
• Public Health Scotland website
• Down's Syndrome Scotland website
• Medical Research Scotland website
• Antenatal Results and Choices website

The implementation and impact of non-invasive prenatal testing (NIPT) for Down's syndrome into antenatal screening programmes: A systematic review and meta-analysis

Sebire E, Rodrigo CH, Bhattacharya S, Black M, Wood R, Vieira R (2024) The implementation and impact of non-invasive prenatal testing (NIPT) for Down's syndrome into antenatal screening programmes: A systematic review and meta-analysis. PLoS ONE 19(5): e0298643. https://doi.org/10.1371/journal.pone.0298643

Press release

Pregnancy Screening for Down's Syndrome, Edwards' Syndrome, and Patau's Syndrome in Scotland

Public Health Scotland Official Statistics in Development: Pregnancy Screening for Down's Syndrome, Edwards' Syndrome, and Patau's Syndrome in Scotland. https://publichealthscotland.scot/publications/pregnancy-screening-for-down-s-syndrome-edwards-syndrome-and-patau-s-syndrome-in-scotland/pregnancy-screening-for-down-s-syndrome-edwards-syndrome-and-patau-s-syndrome-in-scotland/