(11+0 – 13+6 week of pregnancy)
The examination done as part of the first trimester screening includes several components:
Early exclusion of abnormalities
As early as the 1st trimester, many serious abnormalities – particularly concerning the head and brain, the arms and legs, gaps in the abdominal wall and spine, defects of the diaphragm and bladder – can be detected or largely ruled out (early obstetric ultrasound). Furthermore, some of the serious heart defects can be detected by an early heart ultrasound (early fetal echocardiography). In this way risk situations can be detected at an early stage and an optimal management process introduced.
First trimester screening
(nuchal fold scan, nuchal translucency scan, NT screening):
The term NT (nuchal translucency) describes a collection of fluid under the skin between the skin and soft tissue at the back of the baby’s neck. By measuring the NT between the 11+0 and 13+6 week of pregnancy or CRL of 45-84 mm), it should be possible to judge whether there is a statistically increased risk of a child with trisomy 21 (Down’s syndrome), trisomy 18 (Edwards’ syndrome) or trisomy 13 (Patau’s syndrome). If, in all cases with an NT above the 95th percentile, a chromosomal analysis is carried out, around 75 % of pregnancies with a trisomy are detected. A differential risk analysis taking age and previous history into account can increase the detection rate to over 80 %. Combined with two biochemical laboratory values (PAPP-A and free ß-hCG) in the maternal blood, the detection rate is increased another 10 % to 90 %.
Should this result in an increased risk, then we will talk to you and discuss whether and in what form a further direct and possibly invasive diagnosis should be carried out. In this consultation situation, we always pay attention to your individual expectations and wishes.
An enlarged NT can also be found more often than not, however, in babies with a heart defect and a number of other disorders described in literature (e.g. skeletal abnormalities and metabolic defects), so that in case of normal chromosomal analysis, an early organ diagnosis (organ ultrasound) and a detailed examination of the heart (fetal echocardiography) can be arranged.
Studies have shown that, as part of the first trimester screening with a later examination with blood analysis in approx. the 11th week of pregnancy and an ultrasound scan in approx. the 13th week of pregnancy, compared to simultaneously analysing these components (so-called Oscar, one stop clinical assessment of risk), the highest rate of detection can be achieved with ultrasound screening for chromosome anomalies, particularly Down’s syndrome. Furthermore, it is thereby possible to incorporate the so-called second step parameters from advanced screening according to the FMF guidelines (nasal bone, ductus venosus, tricuspid valve flow) in the risk analysis. This is useful if, after the first risk analysis, no assignment to the high-risk or low-risk group is possible, but instead there is a so-called intermediate risk (T21 risk between 1:50 and 1:1000).
The software licence required for the risk analysis is only made available to examiners who have been certified by the Fetal Medicine Foundation, London. Using the risk profile determined by these means, it is possible to customise the decision regarding further diagnostic measures (e.g. organ ultrasound, chorionic villus sampling, amniocentesis). We therefore offer all patients this version of first trimester screening. The overall result can be discussed with the patient immediately after the ultrasound scan.
Naturally these enhanced diagnostic measures can also be carried out by us after an examination carried out elsewhere showing an intermediate risk result.
The test available since 2012 for trisomy 21, 13 and 18 (NIPT) from the mother’s blood cannot replace the first trimester screening, as it is unable to make a statement about other chromosomal defects, genetic disorders or fetal malformations. In certain situations it can be useful as a complement to the first trimester screening. We can advise you about this as part of the ultrasound scan. Before the test can be carried out, a consultation from a specialist for human genetics is also necessary.
Risk of preeclampsia
Preeclampsia and placenta under-function are other risk situations that are estimated at our practice as part of the first trimester screening. In case of increased risk, preventive / therapeutic intervention is possible here and appropriate monitoring of the pregnancy can help to improve the course of pregnancy.