Antenatal Screening

Combined Screening for Down's syndrome & other chromosomal abnormalities: nuchal translucency scan & blood test (low risk results)

All pregnant women in England are now offered tests for Down’s syndrome. The tests can provide information about the chance of a baby having Down’s syndrome. These tests use blood samples taken from the mother, measurements taken from ultrasound scans (nuchal translucency scan/dating scan) or both to work out this chance. The NHS Fetal Anomaly Screening Programme now recommends that women have the combined screening for Down’s syndrome (blood test and nuchal translucency scan) rather than just the blood test or the nuchal translucency scan on its own. The vast majority of units in England, Scotland and Wales now offer combined screening for Down’s syndrome.

Nuchal translucency scans (ultrasound) are normally done between 10- 14 weeks of pregnancy. They measure a small fluid collection within the skin at the back of the baby's neck (nuchal translucency) to help identify the risk of Down's syndrome and other chromosomal abnormalities. The results are combined with a blood test result (combined screening test) to give a more accurate calculation but these tests cannot give a definite diagnosis. If the risk is more than 1 in 150, further tests for Down's syndrome will be offered. If the measurement of the fluid is the same or greater than 3.5mm, women will be advised that this may be an indicator of cardiac or other problems and a referral to fetal medicine specialists will be offered.

The risk of Down's syndrome increases as the mother gets older; the combined screening test assesses your individual risk, and can show whether your risk is higher or lower than for other women of the same age.

Not everyone we talked to had had a nuchal scan. Sometimes it was not offered locally on the NHS, and some people decided they did not want to pay for it privately, particularly if they felt they were low-risk.

One woman chose not to pay privately because she did not get much information till her booking visit, but in any case did not feel she really wanted it. (See also 'Information for making decisions about antenatal screening').

Some people were unsure whether they had had a nuchal scan or just a dating scan. Many were unaware they could have a blood test at the same time. Even amongst those who had been well informed about the options, some commented that the process seemed very rushed. Two people said that they had made their appointment too late for the scan measurements to be reliable.

For women who book too late (after 14 weeks +1 day), for a combined test (blood test and nuchal translucency scan), the quadruple test is offered. (See ‘Blood test screening’ for more information).

For most women who had the nuchal scan, like other scans, it was an enjoyable experience. Many were impressed at how staff took time to explain what they were seeing on the screen and answered questions. The scan gave them their first chance to see the baby, and made pregnancy seem real. This woman also commented on the high quality of the equipment used for nuchal scans at specialist centres. Some women mentioned the discomfort of waiting with a full bladder, and staff pressing uncomfortably hard as they do the scan.

In most cases, people were reassured by their results (see also 'Understanding antenatal screening test results'), but some felt anxious during the scan itself. Reasons for anxiety included staff talking to each other, not to the parents; calling in a senior colleague without explaining why; staff seeming rushed or detached; having to have a repeat scan; and staff remaining or becoming silent without explaining why.

Most people said they preferred to be talked to throughout the scan and have everything explained. (It is worth noting that in some circumstances the person doing the scan may not feel qualified to discuss the results). A woman carrying twins described different levels of communication in two repeat scans and their effect on her.

One person felt she would probably rather receive bad news after the scan than during it. The importance of human warmth was emphasised by a woman who trained as a doctor, as a message for all professionals communicating with pregnant women, in scans and in other settings.

Some people who were reassured by their nuchal scan results later found their baby did have a chromosomal condition, and some people were told they did have an increased chance of something being wrong with the baby.

(See also 'Combined screening for Down's syndrome and other chromosomal abnormalities: nucal scan and blood tests (being told something may be wrong)', 'Understanding antenatal screening test results', 'Deciding whether to have further diagnostic tests' and 'Learning after birth that the baby has a condition').

Many experiences discussed here are common to other types of scan. (See also 'Early dating scans' and '18-20 week scans' ).

Last reviewed July 2017.
Last updated July 2017.


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