Screening for Down syndrome during the first trimester
- Public service
Screening for Down syndrome is based on an ultrasound scan and blood samples from the mother. The screening allows for detection of Down syndrome in a large proportion of foetuses with the condition as early as during the first trimester. Participation in the screening and the possible further examinations is voluntary.
The purpose of the screening is to find the expectant mothers with a higher probability of giving birth to a child with Down syndrome and to steer them to further examinations. This probability is calculated based on the mother's age, the measurement of nuchal translucency determined based on an ultrasound and the content of markers determined from the mother's blood samples. The final probability is calculated by a computer programme, which has been developed for this purpose. A positive screening test indicates that the foetus in question has a higher probability of having Down syndrome.
In five percent of pregnancies, the screening test is positive, i.e. the foetus has a higher probability of having Down syndrome. This five percent groups includes over 80% of all those pregnancies, where the foetus does have Down syndrome. It is good to note that in most pregnancies with a positive screening test, the foetus does not have Down syndrome.
The current method is better than screening based on the mother's age alone, and it can therefore better find those pregnancies with higher probability of the foetus having Down syndrome. The mothers found with the help of this screening can be steered towards further examinations, if they so wish. Further examinations include examining the foetus' cells by taking samples of the placenta or the amniotic fluid. If the foetus is diagnosed with Down syndrome, the family can either prepare for the birth of a child with special needs or decide to terminate the pregnancy, which is possible up until the 24th week of pregnancy, according to Finnish law.
Screening through clinic referral
Screening for a higher risk pregnancy is implemented through a referral from the maternity clinic at the outpatient maternity clinic of the delivery hospital. The invitation to the ultrasound scan is sent from the hospital. A blood sample will be taken during the pregnancy weeks 10-11+6, after which an ultrasound is carried out between weeks 11+0 and 13+6. This ultrasound determines the size of the foetus as well as the measurement of nuchal translucency. After this, a computer program will calculate the...
To whom and on what terms
The service is only for citizens of Helsinki.