Screening

Screening of Down-syndrome from maternal blood

Advantages of the examination

· Mothers over 35 can avoid chorionic biopsy (taking sample from the caul), or amniocentesis (taking sample from amniotic fluid). (These examination mean 1-2%,and around 1% chance for spontaneous abortion)

· Also there are no risk factors in case of women under 35. (Nowadays they gave birth to the majority of babies who suffer from Down-syndrome, because the lack of examination of the foetus.)

· Down-syndrome can be screened with more than 90% likelihood by ultrasound and examination of the maternal blood

· It is simple, free from risk, and fast.

· It does not strain neither the mother nor the foetus

What is Down-syndrome?

It is the most common chromosome abnormality. A normal human cell contains 23 couple chromosomes, but in case of a person suffering from Down-syndrome the cell contains 3 21th chromosomes (trisomy), or the 21st chromosome coheres with an other (translocation).

People who suffer from Down-syndrome are mentally retarded, have a typical appearance, and other symptoms can be heart failure, disorders of the immune system, problems with breathing and predisposition to infections. Some people who suffer from Down-syndrome are able to live quite an independent life, others need maintenance. The seriousness of the disease can be very different but it cannot be detected before birth.

The likelihood of Down-syndrome

Down-syndrome affects 1 new-born from 700 on the average. But the likelihood of chromosome abnormalities is increasing with the age of the mother.

In Hungary the chromosome examination is offered if the mother is older than 35, but it increases the likelihood of spontaneous abortion by 1%. This examination is not done in case of mothers under 35, that is why they gave birth to the majority of babies with Down-syndrome. In these cases they take into consideration only the age and not the personal risk.

International researches have proven that modern screening methods are more beneficial to decide in which cases we should apply invasive diagnostic methods (amniocentesis, CVS /chorionic villus
S

sample/).

Diagnosing the chromosome abnormalities

Chromosome abnormalities can be detected with high certainty (~99%) only by the examination of the foetus. These methods (amniocentesis, CVS, chorionic biopsy) in a small compass risk the life of the foetus. They are called invasive examinations.

Methods which do not risk abortion are ultrasound and biochemical examination of the maternal blood. These methods are not capable of diagnose but we can estimate the likelihood of Down-syndrome with high degree of certainty.

Available methods at our clinic

The primary purpose of these screenings is detecting Down-syndrome but they might detect other developmental disorders such as open neural tube effect, or Edwards’s syndrome.

From the 15^th week of pregnancy:

· ‘Four test’: measuring the amount of 3 maternal hormones (HCG, estriol and inhibin A) and a foetal protein (AFP) in the blood. We take into consideration other circumstances (the age of the mother, smoking etc…) and with statistical methods we calculate the likelihood of Down-syndrome. The optimum time of taking the blood sample is the 16^th week, but it can be taken between the 14^th and 18^th week of the pregnancy.

Before the 14^th week of pregnancy:

· Combined test: measuring the amount of a hormone and a protein (HCG and PAPP-A) in the blood and examination with ultrasound. The CRL and nuchal translucency, the presence of the nasal bone is examined by ultrasound. The optimum time of taking the blood sample is the 12^th week but it can be taken between the 11^th and 14^th week of the pregnancy.

· Integrated test: we make the same ultrasound test, and the measuring the amount of PAPP-A as in the combined test in the 12^th week of the pregnancy. Later, about the 16^th week we measure the amount of AFP, HCG, free estriol and inhibin A markers such as in the ‘Four test’. We take into consideration other circumstances (the age of the mother, smoking etc…) and with statistical methods we calculate the likelihood of Down-syndrome. We estimate the risk only after the second blood test.

The result is an estimation made by a special computer program, which tells us the likelihood of Down-syndrome, or other chromosome abnormalities, and open neural tube effect.

The efficiency of screening methods

All the results base on statistical methods so they cannot be considered as diagnoses. The result is a risk rate which shows the likelihood of the foetus has Down-syndrome.

The performance of our methods is shown in the following chart:

*False positive rate: which percentage of the pregnancies have positive test but a healthy baby

**Sensitivity: the likelihood of the test is positive and the foetus suffers from Down-syndrome

Negative result

If the test is negative it means that the likelihood of Down-syndrome os very low but it does not mean that your baby is certainly healthy. You should see your doctor after a negative test too.

Positive result

The positive result does not mean real problem in most of the cases, so you should not worry. But if the test is positive you have to go to genetic counselling. In that case the examination of the foetal chromosome is necessary.

Who should have these screenings?

All pregnant mothers should have at least one screening.

Before the examination the mothers get all the information they need about the screenings from the adviser of the screening centre.

Reasons which exclude screening

· if you expect twins it is worthy to do only the ultrasound tests

· insulin-dependent diabetes

· vaginal bleeding in 7 days before the screening

· amniocentesis or CVS before the blood sample is taken