Nuchal Scan

The Combined Ultrasound and Biochemistry Scan (CUBS)

This assessment is for women who wish to have a screening test for the prediction of a baby with Down's Syndrome. The test combines the woman's age, the measurement of 2 proteins (biochemical markers) in the mother's blood and a measurement of the skinfold behind the baby's neck (see photo above) at 11 and a half to 14 weeks' of pregnancy. If you are expecting twins then the Down's risk is calculated from the nuchal ultrasound measurement and the mother's age alone.

What is the CUBS test?

The CUBS test is based on the screening test developed by the Fetal Medicine Foundation in London and subsequently pioneered for Scottish women by the consultants who work in the Nuffield and GCRM. The consultants have been trained by the Fetal Medicine Foundation and the biochemical markers are assayed by the Regional Genetics Laboratory in Glasgow.

The test is best performed between 11 and a half and 14 weeks. The scan is similar to the first 'booking' or early pregnancy scan but may take 20-30 minutes because of the additional detail required to make the measurements. The scan is usually best performed with an empty bladder as the consultant may need to press firmly on the abdomen to get the best views of the baby's neck. Very occasionally (<2%) a transvaginal scan may be required in order to obtain accurate measurements.

The results of the first 6000 screening CUBS tests have revealed that the test has a greater than 90% detection rate for Down's syndrome which is appreciably better (more accurate) than the routinely available blood test offered at 15 to 20 weeks. CUBS testing is the current 'gold standard' screening test for Down syndrome; the HeaIth Technology Assessment, an evaluation carried out by the Health Department of the Scottish Executive published in 2004 (www.nhshealthquality.org) has recommended that CUBS testing be made available to all women having babies in Scotland. It is not yet widely available in Scottish maternity hospitals. CUBS testing has been available at the Glasgow Nuffield for over 3 years and is also available at GCRM.

The blood sample will be taken by one of the clinic staff and women will be informed of their results by telephone after 2-4 days. A written report is posted to your address.

The result of the screening test is reported in two ways. Firstly, the result is categorised into a 'low risk' or a 'high risk' result. The cut-off for determining the two risk categories is 1 in 250. Ninety-five percent of women will have a 'low risk' result and no further action is usually recommended. The actual risk of Down's syndrome is also provided; the lowest risk that can be quoted is less than 1 in 20,000 whilst the highest is greater than 1 in 2.

Should a high risk of Down's syndrome be received, your consultant will discuss the implication of the result with you.