Triple test (AFP, ß HCG, free estriol)

Triple test of the second trimester of pregnancy Held at 16-18 weeks of pregnancy. In the blood of a pregnant woman Concentration of three hormones — Free chorionic gonadotropin (β-hCG), Alpha Fetoprotein (AFP) და Unconjugated estriol (UE3) Will be determined. Ultrasound examination of the test determines the biparietal diameter of the fetus, the size of the femur and the circumference of the head.

Prenatal screening in the second trimester is necessary:

• To assess the risk of developing a neural stem defect;
• In pregnant women who have consulted women late;
• To conduct integrated testing, which integrates data obtained in the first and second trimesters of pregnancy.

Screening is based on the analysis of substances (markers) produced by the fetus and placenta in blood serum; The results obtained for these markers, along with some of the mother's clinical data (maternal age, gestational age, weight, race, diabetic status, smoking, artificial reproductive interference) are used to calculate the risk through special computer programs.

The laboratory sets a limit of values ​​for each anomaly; Increased risk indicates that the data obtained exceeds the established limit, but has no diagnostic value, but indicates the possibility of conducting additional studies.

Screening in the second trimester of pregnancy varies according to the number of markers studied: Triple test (AFP, estriol, hCG) ან Quadruple test (AFP, estriol, hCG, inhibin A).

The triple test includes:

• Identification of three markers in maternal serum: free chorionic gonadotropin (β-hCG), alpha fetoprotein (AFP), and unconjugated estriol (UE3).
• Calculation of MoM (median variable) for each marker (the result of the marker is divided by the mean value corresponding to gestational age);
• MoM correction according to pregnant covariates;
• Determining the risk of Down syndrome (calculated on the basis of MoM, adjusted for each marker and age of the mother).
• Risk of developing neural stem defect (calculated on the basis of MoM adjusted for AFP);
• Trisomy 18 risk assessment (calculated based on MoM, adjusted for each marker and age of the mother).
• Determining the risk of other fetal aneuploidies (trisomy 13, Turner syndrome, triploidy) or Smith-Lemmel-Opis syndrome (SLOS) if a specific type of fetal abnormality has been established during a previous pregnancy;

Serum markers:

AFP Is a protein that is synthesized mainly by the fetal liver. AFP concentrations during pregnancy gradually increase from 0.2 ng / ml to 250 ng / ml at 32 weeks of gestation.

AFP (MoM) levels are higher in pregnant women associated with fetal neural tube defects (anencephaly, spina bifida, encephalocytosis), and lower than average in Down syndrome, trisomy 18 and 13.

Unconjugated estriol Produced in the fetoplacental unit. Its level in the serum of pregnant women gradually increases during pregnancy and is usually low during pregnancy, which is associated with Down syndrome and trisomy 18.

Estriol is also low in pregnant women associated with Smith-Lemmel-Opis syndrome (a syndrome characterized by mental retardation and many congenital defects based on a significant disruption of cholesterol synthesis), fetal anencephaly, Turner syndrome, and fetal edema.

In the second trimester of pregnancy Β subunit of free chorionic gonadotropin (β-hCG) - Considered a more relevant marker than the intact HCG molecule. In pregnant women with Down syndrome, β-hCG levels are> 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 triploidy, the concentration of free β-hCG is significantly lower.

When should we take the triple test? 

A triple test is recommended for all pregnant women at 16-18 weeks. Tests are especially important if the following factors are present:

• Pregnant age - 35 years and over.
• Existence 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, 13 are observed during the ultrasound examination.
• If the father has Robertson translocation.

How to prepare for the test? 

Triple test can be performed at 15-20 weeks of pregnancy + 6 days (optimal period: 16-18 weeks).

Women do not need to prepare for the triple test. The test can be performed both on an empty stomach (on an empty stomach) and after a meal (there are no restrictions on food and drink).

A triple test is required Venous blood.

Possible interpretation of the results

Down Syndrome and Trisomy 18

Low risk: The calculated risk values ​​are less than the set values ​​limit.

The resulting "low risk" result does not rule out the presence of Down syndrome or trisomy 18.

The incidence of Down syndrome is 63% for cases where gestational age is calculated based on the date of the last menstrual period, and 70% for cases where ultrasound data are taken into account in the calculation. In the case of trisomy 18, the detection rate is 60-80%.

Increased risk: The calculated risk rate exceeds the set limit.

"Increased risk" does not determine the diagnostics of trisomy 21 or 18, but requires additional studies (amniocentesis and chromosomal analysis).

Described False positive results - 5% and 0.2% of trisomy 18 in Down syndrome.

Other definitions of increased risk are: miscalculation of gestational age or the presence of other chromosomal abnormalities.

Nerve stem defects

Low risk: The calculated MoM value for AFP is lower than the 2.5 MoM AFP threshold.

Low risk does not rule out the presence of nerve stem defects.

Increased risk: The calculated MoM value for AFP exceeds the 2.5 MoM AFP threshold.

"Increased risk" does not confirm the diagnostics of nerve stem defect, but indicates the need for additional research.

Described 3% False positive result Case.

Other definitions of "increased risk" include miscalculation of gestational age, multiple pregnancies, chromosomal abnormalities, structural disorders of the placenta, abdominal wall defects, and recent placental bleeding.

The triple 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.

Additional examinations include: genetic counseling, ultrasound, amniocentesis by chromosomal analysis, and AFP determination in amniotic fluid.

*** The test is done once a week - on Tuesdays