First trimester screening: when? Costs?
The so-called first trimester screening is an examination in the first trimester of pregnancy and is used to detect chromosomal abnormalities such as Down syndrome. Here you can find out what happens during the first trimester screening, when it is carried out and how it is to be interpreted.
When is a first trimester screening done?
First trimester screening is a low-risk method of assessing the likelihood of a chromosomal abnormality in the baby. The most well-known chromosomal disorder is trisonomy 21 , better known as Down syndrome. However, first trimester screening is not an integral part of the prenatal care mandated by maternity guidelines . It is an optional examination and is not paid for by statutory health insurance companies.
What happens during the first trimester screening?
The first trimester screening is carried out between the 12th and 14th week of pregnancy. It combines the following test results and data:
- Nuchal translucency measurement : This is a special ultrasound examination that can be carried out between the 11th and 14th week of pregnancy. During this time, fluid builds up in the baby’s neck area. This edema (technical term for fluid accumulation) is measured. If the nuchal fold is significantly enlarged (> 3 mm), this observation indicates a higher statistical probability that the child will be born with a chromosomal anomaly (eg Down’s syndrome). Learn more about this test in our post “Nuchal Translucency Measurement ” .
- Blood test PAPP-A and free ß-HCG : The pregnancy-related proteins PAPP-A and free ß-HCG are determined in the maternal blood. A blood test is carried out for this. Statistically, the PAPP-A value is significantly lower in pregnant women whose babies suffer from Down syndrome, while the ß-HCG value is significantly higher.
- The age of the pregnant woman is taken into account when calculating the probability. The risk of a chromosomal abnormality increases especially in women over the age of 35. For comparison: in a pregnant woman at 25, the probability of having Down syndrome in the child is 1:1350, in a 35-year-old 1:380, in a 40-year-old 1:100.
- The inclusion of the exact week of pregnancy leads to a more precise result in the calculation.
Figure Nuchal translucency measurement
In addition, the baby is examined for other indications:
- Anomalies in the nasal bone
- So-called plexus cysts (harmless cystic structures without any pathological value in their own right in the area of the choroid plexus in the brain)
- White spots on the heart (punctiform compressions in the right, but more often in the left large ventricle or in both ventricles of an unborn child). White spots usually regress spontaneously.
- Enlarged renal pelvis
- Bladder too large
- Abnormal ultrasound echo of the bowel or femur that is too short
Using the values, the doctor or the laboratory then uses a computer program to calculate the probability of the presence of a chromosomal abnormality.
Detection rate of first trimester screening
The detection rate for trisomy 21 improves the more factors are included in the risk calculation. If only the nuchal fold measurement is carried out or only the laboratory parameters PAPP-A and free ß-HCG are taken into account, a chromosomal disorder is correctly identified or correctly ruled out in about 70 percent of all cases. However, if the results of the nuchal translucency measurement and the laboratory parameters PAPP-A and free ß-HCG are included in the probability calculation together with the age of the mother, a chromosomal disorder can even be detected or ruled out with a probability of 80 to 90 percent. This means that in only 10 percent of all cases after the first trimester screening a chromosomal disorder remains undetected.
| Factors involved | Detection Rate for Down Syndrome |
|---|---|
| age | 50% |
| Age + PAPP-A/ ß-HCG | 70% |
| Age + nuchal translucency | 70% |
| Age + PAPP-A/ ß-HCG + nuchal translucency | 80% – 90% |
Interpret results of first trimester screening
Please remember: the concept of first trimester screening is only a statistical risk calculation. This series of tests cannot offer 100% certainty. But especially women with an unremarkable pregnancy, this screening can give further confidence in the health of their child. Unfortunately, an inconspicuous finding cannot completely rule out a fetal chromosomal disorder. Just as little as a conspicuous finding can prove this. A noticeably large neck fold can also be caused by other malformations and diseases, it does not necessarily have to be an indication of Down syndrome. Heart defects, metabolic disorders or, for example, a diaphragmatic or umbilical hernia can also have caused this enlargement. In the case of a conspicuous finding, achorionic villi biopsy or amniocentesis provide security. If, contrary to expectations, you should receive a conspicuous finding, your gynecologist will advise you in detail on further measures.