Double test (PAPP-A, free ß-HCG)

Double screening test for the first trimester of pregnancy Is done for early detection of the risk of fetal genetic disorders and Mother's blood და Ultrasound examinations of the fetus includes. Both of them are definitely held on the same day. The mother's ethnicity, age, weight, bad habits and medical history should be considered at this time.

The obtained results are processed by a special computer program. It has fetal chromosomal abnormalities - Chromosome 21 (Down Syndrome), I-Chromosome 13 (Pataus Syndrome), Chromosome 18 (Edwards Syndrome) და Nerve stem defect Of existence Allows risk assessment.

The first trimester of pregnancy or a double test of pregnancy Held at 11-13 weeks. As a result, the concentration of two hormones in the blood of a pregnant woman - Free chorionic gonadotropin (β-hCG) და Pregnancy-associated blood plasma protein A (PAPP-A) Will be determined. To perform the test, the ultrasound examination determines the size of the fetal coccyx, the thickness of the neck crease and the size of the nasal bone.

The first trimester biochemical screening (double) test includes:

• Determination of serum markers PAPP-A and free (β-hCG).
• Calculation of MoM (median variable) for each marker (the result obtained by the marker is divided by the mean value corresponding to gestational age).
• MoM correction according to pregnancy covariates.
• Determination of biochemical risk of Down syndrome at birth (calculated on the basis of MoM, adjusted for each marker and age of the mother).
• Determining the risk of developing trisomy 18 at birth (calculated based on MoM, adjusted for each marker and age of the mother).
• Determining the risk of developing trisomy 13 at birth (calculated based on MoM, adjusted for each marker and age of the mother).
• Calculation of MoM for fetal cervical space (neck wrinkle) (if physician provides ultrasound data to laboratory).
• Ultrasound examination or non-visualization of the nasal bone is also included in the prenatal risk calculation algorithm.
• Combined risk of Down syndrome (biochemical risk + ultrasound parameters).
• Risk of developing other aneuploidies of the fetus (Turner syndrome, triploidy) if the doctor / patient informs the laboratory about the existence of a previous pregnancy with a certain type of chromosomal pathology.

Serum markers:

PAPP-A (Pregnancy-Related Plasma Protein) Is a glycoprotein derived from the placenta. During pregnancy it is produced in large quantities by trophoblasts and enters the mother's bloodstream. Serum levels of this protein increase with gestational age, reaching a peak at the end of pregnancy.

Recent studies have shown that decreased PAPP-A levels during pregnancy are associated with chromosomal abnormalities in the fetus: trisomy 21, 18, 13, Turner syndrome, paternal triploid (minor impairment), maternal triploid (significant impairment).

In the first trimester of pregnancy Β subunit of free chorionic gonadotropin (β-hCG) - is considered a more relevant marker than the intact HCG molecule. Β-hCG level in pregnant women with Down syndrome> 2 MoM. The rates are also much higher for triploids of paternal origin. Free β-hCG levels are normal in Turner syndrome. In the presence of trisomy 18 or 13 as well as maternal triploid, the concentration of free β-hCG is significantly lower.

When to take a double test?

A double test is recommended for all pregnant women at 11-13 weeks. Tests are especially important if the following factors are present:

• Pregnant age - 35 years and over;
• The presence of congenital defects in the family history;
• Use of high-risk medications during pregnancy;
• If a pregnant woman has diabetes;
• If you have a viral infection during pregnancy;
• If the woman was exposed to radiation;
• If abnormalities associated with trisomy of chromosomes 21, 18 and 13 are noted during the ultrasound examination;
• If the father has Robertson translocation.

How to prepare for the test?

A double test is required Venous blood.

The test is performed fasting or postprandially (after eating).

Possible interpretation of the results

Low risk: The risk data calculated at this time are less than the set limit.

Low risk does not completely rule out the presence of Down syndrome, trisomy 18 or 13.

Increased risk: The calculated risk data exceeds the set limit. The "increased risk" obtained is not a confirmed diagnostics of trisomy 21, 18, or 13, but requires further investigation.

The double test is not a diagnostic method. In the event of an increased risk of fetal anomaly, the obstetrician-gynecologist will decide whether to perform an additional examination: biopsy of the chorionic villus (I trimester) or amniocentesis (II trimester) and further cytogenetic examination.