Prenatal screening tests

Research in the Department of Obstetrics and Gynecology focuses on the prenatal diagnosis of syndromic and non-syndromic congenital malformations. The center provides prenatal biochemical and ultrasound screening services in the first trimester (Double test) and second trimester of pregnancy (Triple Test).

The double test

Dublul test (testul combinat)

Double test includes biochemical markers analysis from maternal blood: PAPP-A, hHCG + TN (as assessed by ultrasonography) by calculating the median gestational age appropriate for each marker in first trimester of pregnancy (in week 11-13 + 6 days).

The purpose of this test is the determination of PAPP-A, TN and free hCGβ and used to calculate the mother’s risk to have a fetus with chromosomal abnormality (Down’s syndrome, Patau and Edwards).
PAPP-A (pregnancy-associated plasma protein A) is a glycoprotein wich is secreted from the trofoblastic tissues of the placenta and released into the blood, taking a role in the growth of the fetus.
Human chorionic gonadotropin (hCG) is a glycoprotein that consists of 2 subunits: alpha and beta. Is produced by syncytiotrophoblast cells of the placenta, very early in pregnancy and is intended to maintain the corpus luteum and progesterone production in the first trimester of pregnancy.

Serum PAPP-A is decreased on average in pregnancies affected by Down’s syndrome and free hCGβ in serum is increased over two fold on average in pregnancies affected by Down’s syndrome and also reduced in pregnancies affected by Edwards’ syndrome, Nuchal Translucency(NT) is also bigger in pregnancies affected by Down’s syndrome.

The triple test

The triple test

The second trimester of pregnancy screening (week 15-19 + 6 days) is conducted by evaluating the markers: AFP, ESTRIOL and free beta HCG in the mother’s blood to calculate the risk for chromosomal abnormalities and neural tube defects.

Human alpha-fetoprotein (hAFP) is a glycoprotein of fetal origin, synthesized by the embryonic yolk sac cells and later by the fetal liver.
In unaffected pregnancies, the level of AFP increases with gestation in maternal serum and decreases in amniotic fluid. AFP can be used in screening for neural tube and abdominal wall defects.

The low AFP level indicates the presence of Down, Edwards, Patau syndrome in the fetus and its increase indicates neural tube defects such as spina bifida or anencephaly.
Estriol (uE3) is a steroid of feto-placental origin. In the maternal serum, estriol can be measured in unconjugated form.
Decreasing uE3 in maternal blood is a suggestive marker for Down syndrome, Edwards, or neural tube defects.

If a test is positive for a genetic syndrome it is necessary to confirm the diagnosis by definitive tests, genetic testing by the method

Q.F.-P.C.R. (Analysis of chromosomes 13, 18, 21, X and Y)

is indicated for pregnant women with modified double-triple test results or if the woman is aged 35 years or older. QF – PCR detects the most common abnormalities (Down syndrome, Edwards syndrome, Patau syndrome, Turner syndrome, Kinefelter syndrome and triploidies).

Or

G-band staining
is a chromosome-staining technique used in human cytogenetics to identify individual chromosomes, which produces characteristic bands. It utilizes acetic acid fixation air drying, denaturing chromosomes mildly with proteolytic enzymes, salt heat, detergents or urea and finally Giemsa stain.


Methodology

Serum markers are determined by the “time-resolved fluoroimmunoassay TR-FIA” immunofluorimetric method, where fluorescence ions are used for labeling. They are linked to sandwich antibodies – over a period of several minutes to form a homogeneous and strongly fluorescent chelating solution. The solution allows highly sensitive determinations of the Eu and implicitly of the serum markers observed.

The inducer dissociates the Europion ions from the labeled antibodies in the solution, where they form strong fluorescence chelates with the inducer components. The fluorescence in each cup is then measured. The fluorescence in each sample is inversely proportional to the concentration of uE3, PAPP-A, AFP and free hCGβ.


Highlights

  • Prenatal screening = serum determination of non-invasive fetal and placental analytes;
  • The laboratory sets a cut-off for each analyte; An increased risk does not indicate that the fetus is affected and for a firm diagnosis additional investigations should be made such as: corial villous biopsy in the first trimester of pregnancy and amniocentesis in the second trimester of pregnancy.

The departments were considered to be involved in educational and research projects at the University and Postgraduate Levels (PhD, postdoctoral studies, post-graduate studies).

 

* Information are taken from instructions to use kit’s reagents used in the testing of biochemical markers.