It is possible to detect many serious abnormalities – especially of the head, the brain, the arms and legs as well as openings in the abdominal wall and the backbone, and defects in the diaphragm and the urinary bladder, already during the first trimester of pregnancy (early organ screening). Moreover, it is possible to detect some severe heart defects by an early heart ultrasound (early fetal echocardiography).
First trimester screening (nuchal fold measurement, nuchal translucency measurement, NT-screening):
The nuchal translucency is a collection of fluid beneath the fetal skin in the region of the fetal neck. Measuring nuchal translucency between week 11+0 and 13+6 of pregnancy (crown rump length between 45-84 mm) helps to identify pregnant women with a statistically high risk for a baby with trisomy 21
(Down syndrome), trisomy 18 (Edwards syndrome) or trisomy 13 (Patau-Syndrom). If in all cases where the NT thickness is defined as being above the 95th centile of the normal range a chromosomal analysis is performed, approximately 75% of fetuses with trisomy 21, 18, or 13 are identified. Sophisticated risk assessment considering maternal age and medical histories may increase the detection rate to over 80%. Using all these results in combination with two maternal serum levels (PAPP-A and free ß-hCG) results in an improvement of 10% in detection efficiency, giving a detection rate of 90%. Increased nuchal translucency in chromosomally normal fetuses is associated with an increased prevalence of major cardiac defects and a variety of other diseases described in literature such as skeletal abnormalities and disorders of metabolism, and, as such, is an indication for specialist fetal echocardiography (early organ diagnosis and detailed examination of the heart).
Recent studies have demonstrated that first trimester screening in combination with a time-shifted blood analysis in week 10 of pregnancy and ultrasound screening in week 13 (approximately) has the highest detection rate for pregnancies with chromosome abnormalities, especially the Down syndrome, compared to the simultaneous analysis of all components called Oscar (one stop clinical assessment of risk). Moreover, it is possible to include the so-called second-step parameters examined during the second line screening according to the FMF standards (nasal bone, blood flow in the ductus venosus and across the tricuspid valve, facial angle) into the risk analysis. The results can immediately be discussed with the patient after the ultrasound examination.
Thus, from now on, we offer this kind of first trimester screening to all of our patients.
Only sonographers who have been certified by the Fetal Medicine Foundation
, London are entitled to receive free of charge the FMF software for the calculation of risk of chromosomal abnormalities
. Using the established risk profile, it its possible to decide individually if further diagnosis such as organ screening, chorionic villus sampling, or amniocentesis is needed.
Risk groups for screening for Down syndrome
- High risk: >1:50 An invasive diagnosis is recommended (AC/CVS)
- Intermediate risk: between 1:50 and 1:1000 second step examination is recommended (see below)
- Low risk: < 1:1000 no more measures are necessary?
Intermediate risk (between 1:50 and 1:1000) and second step: If the risk cannot clearly be defined as being high or low risk, additional markers (assessment of the nasal bone, blood flow in the ductus venosus and across the tricuspid valve und FMF- Frontomaxillary facial angle) can be included in the risk evaluation (second step of first trimester screening). We provide examination of these markers besides early organ and heart ultrasound during first semester screening.
Of course we carry out these examinations also for external patients with intermediate risk.