MATTACE RASO DR. FLAVIO - Milan and Melegnano

Bitest - Test Combinato - Duotest - Dualtest - Ultrascreen

bitest / combined test / duotest / dualtest / ultrascreen

(and nuchal translucencyAnd)

PRENATAL SCREENING TESTS: HOW AND WHEN TO PERFORM THEM

The Bitest, Combined Test and Duo Test It is a prenatal screening test first trimester combining ultrasound data and blood chemistry resultsTo estimate the risk of chromosomal abnormalities in the fetus. This non-invasive test does not expose the mother or the baby to the risk of miscarriage and can be offered to all pregnant women, regardless of age. The goal is not to make a diagnosis, but to provide a probabilistic risk assessment, useful for deciding whether further investigation with invasive tests such as chorionic villus sampling or amniocentesis is appropriate.


It is performed in the first trimester of pregnancy, in a well-defined time window.

  • The blood sampling It is usually performed starting from the 10th week.
  • THE'ultrasound with nuchal translucency measurement is performed between the 11th and 13th week 6 days, when the crown-rump length of the embryo falls within a specific range (about 45–84 mm).

    • This timing allows for reliable ultrasound and biochemical data, which are essential for risk assessment. The Bitest is part of the first-trimester screening program and is scheduled in consultation with the gynecologist following the pregnancy.

what is it for?

combined test

The Bitest combined test It is designed to estimate the risk that the fetus is affected by one of the main chromosomal trisomies, in particular:


  • trisomy 21 (Down syndrome)
  • trisomy 18 (Edwards syndrome)
  • trisomy 13 (Patau syndrome)

Based on the combination of nuchal translucency, biomarker values, and maternal characteristics, the test achieves high sensitivity, with the ability to identify a significant proportion of at-risk pregnancies. Furthermore, an increase in nuchal translucency or certain specific combinations of results may also be a warning sign for congenital heart disease, fetal malformations, skeletal abnormalities, or certain genetic syndromes.

It is important to underline that the combined Bitest test provides a statistical risk, expressed in probabilistic form, and not a "yes/no" result: a low-risk outcome reduces the probability of chromosomal abnormalities, but does not eliminate them; a high-risk outcome does not automatically mean that the fetus is affected, but indicates the opportunity to evaluate further investigations.

results and risks

How it works, Risk calculation and interpretation of the result

The Bitest combined test It involves two main steps, which are non-invasive and well tolerated:


  1. Obstetric ultrasound with nuchal translucency measurement
    During an abdominal ultrasound, the thickness of a thin layer of fluid located between the skin and the spinal column at the nape of the fetus's neck (nuchal translucency) is measured. An increase in this thickness is associated with a higher risk of chromosomal abnormalities and certain malformations.
  2. Maternal blood sampling
    At the same time or shortly thereafter, a blood sample is taken to measure two markers produced by the feto-placental unit:
    • PAPP-A (pregnancy-associated plasma protein A)
    • Free β-hCG (beta fraction of human chorionic gonadotropin)


      • The combination of ultrasound and biochemical parameters allows us to build a more accurate picture than using a single data point.

      The data collected during the Bitest combined test They are analyzed using dedicated software. In addition to nuchal translucency, PAPP-A, and β-hCG values, various maternal factors are considered, such as:


      • age of the pregnant woman
      • gestational age
      • weight
      • smoking habit
      • ethnicity
      • possible recourse to medically assisted procreation techniques
      • obstetric history (previous pregnancies)


        • The processing provides a statistical risk of chromosomal abnormalities, expressed as a ratio (e.g., 1 in 500, 1 in 1000) or percentage. The result is compared to a cutoff value to distinguish between increased-risk and reduced-risk situations.


        • A low-risk outcome indicates that the probability of chromosomal abnormalities is lower than the threshold considered, although it does not eliminate it.
        • A increased risk outcome suggests a probability higher than the reference value and may lead to the proposal of invasive confirmatory tests, such as chorionic villus sampling or amniocentesis.


          • It should be remembered that there are false positives and false negativesThe test may indicate an increased risk in the presence of a healthy fetus, just as a reduced risk does not completely rule out a pathology. For this reason, the result should always be interpreted by the gynecologist in the overall clinical context.

advantages and limitations

The Bitest combined test offers the advantage of being an exam:


  • non-invasive
  • can be performed in the first trimester
  • based on objective ultrasound and biochemical parameters


    • Compared to invasive diagnostic tests, it does not carry any procedure-related risk of miscarriage, but only provides a probabilistic estimate. A result indicating a higher risk is not equivalent to a diagnosis, but rather represents a signal to evaluate the need for further testing. In cases of increased nuchal translucency with normal chromosomal makeup, closer ultrasound monitoring may be recommended, possibly with fetal echocardiography and second-level ultrasound between the second and third trimester, to rule out cardiac malformations or other structural abnormalities.

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