Center for Medical Genetics Ltd – Specialized Center for Prenatal Diagnosis
Karel Čutka, MD, David Čutka, MD, Novohradská 68/1806, České Budějovice
Biochemical screening – the Integrated Test
The first blood samples can be taken from all patients from the 10th completed week of pregnancy (10+0 - 11+3). Biochemical parameter PaPP-A is collected.
In case of an extremely low PaPP-A level (approx. 2% of women) it is possible to do a nuchal translucency (NT) scan in the 13th week of pregnancy in our accredited center and to detect an eventual pathology already in the 1st trimester. The vast majority of women come for a second blood test starting week 14+0 (AFP – alpha fetoprotein, HCG - chorionic gonadotropin and uE3 - unconjugated oestriol).
This is called the serum integrated test. In case there is a NT (nuchal translucency) scan done by an accredited sonographer it is possible to put the NT scan and the serum integrated test together. Such a test is then called the integrated test.
The integrated test is the best test for detecting chromosomal anomalies including Down syndrome (the highest detection rate with the lowest number of invasive procedures).
The result is available from the week 14+0, for approx. 5% of women the test is positive. These women are offered amniocentesis in order to check the chromosomal make-up of a fetus. The test takes account of patient’s age, duration of pregnancy, multiplicity of pregnancy, patient’s weight and medians of a laboratory which makes the analysis (a comparison to dozens of patients examined in the past). A chromosomal anomaly can be suspected when PaPP – A, AFP and uE3 levels are lower and when hCG and NT levels are higher.
The risk is calculated by a computer program called ALPHA. In case of an increased level of AFP there is a suspicion for open neural tube defects and abdominal wall defects. Such a suspicion resulting from the test does not mean a definite presence of a congenital anomaly in a fetus; however, it gives a patient a reason for a more thorough prenatal examination, usually amniocentesis and a detailed ultrasound.
- integrated test – detection level of 93 %, the most effective test (biochemical parameters + NT ultrasound scan performed by an accredited sonographer only)
- serum integrated test – detection level of 90 %, analysis of biochemical parameters (in case it is not possible for an accredited sonographer to do the NT scan in population)
- first-trimester test (combined test) – detection level of 83 %
- quadruple test (triple test in the Czech Republic) for women who come to be tested only in the second trimester