Combined test
The combined test calculates the risk of a baby with Down’s syndrome on the basis of three factors:
- The age of the mother
- The levels of two hormones in her blood (PAPP-A and free beta-HCG)
- Three features of the baby – nuchal fold, nasal bone and heart valve – which are visible on ultrasound
Frequently asked questions:
- When is the combined test carried out?
- What happens in the combined test?
- How reliable is the combined test?
- What are the risks for the baby?
- When is the result of the combined test available?
- How much does the combined test cost?
When is the combined test carried out?
Since 1 July 2017 the blood sampling for the combined test (to determine the hormone levels) is only still permitted by the Ministry of Public Health after two NIPTs have not given a definitive answer. As a result of this, in practice the test is only carried out between the twelfth and the fourteenth week of the pregnancy. A NIPT is indeed only reimbursed from the twelfth week.
What happens in the combined test?
- The nuchal fold measurement takes place during the first trimester ultrasound, between around 11 and 13 weeks of pregnancy. In this ultrasound the fluid layer under the skin of the neck of the baby is measured carefully. In babies with Down’s syndrome, but also in other hereditary and non-hereditary conditions, there may be a greater accumulation of fluid present in the neck. The nuchal fold thickness is therefore not only an indicator for Down’s syndrome but also for other abnormalities.
- Furthermore the calcification of the nasal bone is examined as well as the action of the heart valve. Babies with trisomy 21 have slower calcification of the nasal bone and often a leak in the heart valve.
- The combination of your age, your blood picture and the ultrasound characteristics of the foetus lead to a certain risk factor. You have an increased risk if that number is equal to or greater than 1 in 300 (e.g. 1 in 110).
How reliable is the combined test?
The combined test has a sensitivity of 80 to 85%: out of 100 babies with trisomy 21 the test will detect around 85 and miss 15.
In five per cent of cases the combined test is false positive. That means that if 100 women have the test carried out, five women have an increased risk passed on whereas the baby does not have trisomy 21.
What are the risks for the baby?
The combined test is in itself a non-invasive screening test. The blood sampling and ultrasound pose no risk for the pregnancy.
In view of the fact that in five per cent of women the test is false positive, you have a one in twenty chance of having an invasive test, with increased risk for the baby, whereas it does not have trisomy 21.
When is the result of the combined test available?
If the blood has been taken beforehand, the sonographer can calculate the risk immediately after the ultrasound and inform you.
If the blood is taken on the day of the ultrasound and the result is ‘abnormal’, you are informed of this within a week by your gynaecologist or by the sonographer.
How much does the combined test cost?
The health insurance scheme reimburses the combined test only if and after two NIPTs have been carried out which have not given a definitive answer.
For the ultrasound you pay the non-refundable medical expenses of a standard pregnancy ultrasound.
If you do not have any Belgian national health insurance, it will cost you:
- For the blood analysis around 25 euros
- For the ultrasound also 25 euros