Patients' Information

What You Should Know

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What You Should Know
Certified Gynaecologists
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  Chromosomal aberrations in the first third of pregnancy
This information leaflet is designed to acquaint expectant mothers with the possibilities of first-trimester screening. It is important because every pregnant woman runs a certain risk of giving birth to a child with a physical or mental handicap. In many cases, the handicap is due to chromosomal aberration. Chromosomes carry genetic information. The most common and best-known disorder is Down`s Syndrome (so-called "mongolism"). The risk of developing this disease increases with the mother`s age.
An ultrasound examination performed in the early stages of pregnancy, i.e. at week 11 - 14, in combination with a biochemical analysis of the mothers blood sample, allows to evaluate the individual risk level of developing certain chromosomal aberrations. The following examinations are required to this end:
  Nuchal translucency (also called "NT" or "neck fold")
Nuchal translucency thickness (also called NT or "neck fold thickness") is determined by performing an ultrasound scan of the fetuss neck. Low nuchal translucency values are categorised as normal. However, as nuchal translucency increases, so does the risk of the fetus to develop a disease. The examination requires a high-resolution ultrasound device and an experienced examiner. When measuring nuchal translucency, the length and heart rate of the fetus are also examined in order to screen for malformations.
In addition, two pregnancy hormones (free beta-hCG and PAPP-A) can be analysed from the mother`s blood sample. Certain changes in their concentration, evaluated in relation to a statistically determined normal level of concentration (the so-called median value), must be interpreted as an indication of chromosomal aberrations. Based on the mother`s age risk, the biochemical and the ultrasound data are considered together in order to determine the overall risk.
Only a combination of ultrasound data and biochemical measurement will yield a reliable result!
  What does the test result mean?
The test statistically identifies risk groups. Some five percent of all examinations performed may indicate a suspicious result. The test cannot make a conclusive diagnosis, however, up to 90 percent of all trisomy 21 pregnancies are allocated to a risk group. A suspicious test result is not necessarily indicative of a pregnancy with chromosomal aberration. It only states that this pregnancy must be assigned to a risk group. In this case, specific follow-up examinations may be performed.

On the other hand, however, an unsuspicious result does not constitute an absolute guarantee for the birth of a child without chromosomal aberration. A definite exclusion is only possible by means of a direct chromosome analysis! By the same token, an unsuspicious test result does not constitute an absolute guarantee that the child to be born will be free of chromosomal abnormalities. Only direct chromosome analysis can bring the certainty of definite exclusion.
  What to do in case of an increased risk?
If an increased risk has been identified, you should confer with your gynaecologist and then seek advice at a genetic counselling centre in order to discuss options for further diagnostic testing. Following careful genetic counselling, a prenatal diagnostic procedure may be performed which will yield an accurate result in the case of chromosomal aberration. In order to shorten the waiting period, a rapid prenatal test (FISH test) can be carried out in many cases which will provide a result within only one or two days. This allows shortening the usually stressful waiting period considerably.
In the vast majority of cases, the test result is unsuspicious. However, in the case of an increased nuchal translucency with at the same time unsuspicious results of chromosome analysis, a further ultrasound examination should be conducted at about the 20th week of pregnancy so that heart defects and other non-chromosomal anomalies can be excluded.