Неинвазивна ултразвукова пренатална диагностика


e.g.first trimester ultrasound

  • No risk of miscarriage
  • Tentative results
Неинвазивна пренатална диагностика


Molecular, genetic test (e.g. PrenaTest™)

  • No risk of miscarriage
  • Accurate result
Инвазивни методи за пренатална диагностика


Amniocentesis, Chorionic villus sampling

  • Risk of miscarriage – about 1%
  • Accurate result

May be the most grievous and painful news for two parents is to understand that their unborn child, shall be delivered with disorders or with a (severe) lifelong disease. In order to give the parents complete information on the issue, the contemporary healthcare systems provide prenatal screening (PS) to all pregnant women.

The programs for prenatal screening and prenatal diagnostics serve for identifying the potential pregnancy-related risks – both for the mother and for the child. They includemethods and techniques that allowvariousabnormalities (morphological or functional) in the normal development of your babyto be detected before its birth.

In the event the results from such screening and from the subsequent diagnostic procedures are positive for specific genetic abnormalityor other health problem, they should be the grounds for an informed decision for therapy, which the family should take together with the attending gynaecologist or specialists in genetics.

It should by no means be considered as just a medical procedure, which is the most common attitude of the society and the patients, because PS has strong legal, social and ethical concerns.In certain cases it could be thegrounds for the necessity to make the most difficult decision – whether to preserve the future life or not. This is not just a personal and/or medical choice. It is rather a deeply philosophical question about “Which life is /not/ worth living?”, as Ina Dimitrova writes in her book “Prenatal Diagnostics and Biopolitics in Bulgaria”

Type of tests


  • PrenaTest™ – molecular genetic testing of maternal blood
  • Biochemical serum screening
  • Ultrasound screening (US Scan) – fetal anatomy (morphology), etc.


  • Amniocentesis (AC)
  • Chorionic villus sampling (CVS)
  • Cordocentesis (PUBS)
  • Fetoscopy, etc.

The attending physician and the PS specialists may recommend different methods for analysis, depending on the specific PS purpose and the risk characteristics of the pregnancies tested. Each PS method is applied in a specific period during pregnancy, has specific sensitivity in detecting certain congenital abnormalities and genetic defects, and is associated with specific manipulation-related risks.

When are the prenatal screening (PS) examinations carried out?

PrenaTest™ –molecular genetic testing of maternal blood

This test isperformed after the9th week of pregnancy, as currently it identifies the presence of Trisomy 21 (Down’s syndrome), Trisomy 18 (Edward’s syndrome), and Trisomy 13 (Patau’s syndrome) in the unborn. Apart from its screening function, it can be used for determining the baby’s gender at an unprecedented early stage of pregnancy.

0 %

The exact percentage of


Of the PrenaTest™

Early biochemical serum screening

The early biochemical serum screening (EBSS) is a test that is performed in the period between the 11 and 14 weeks of pregnancy, and gives the pregnant women assessment of the risk of chromosomal abnormalities in the unborn: Down’s syndrome (Trisomy 21), Edward’s syndrome (Trisomy 18), Patau’s syndrome (Trisomy 13), Turner syndrome (Monosomy X), and Triploidy. The results from the BSSare in the form of calculated risk score of the type 1:1000. In case of high riskscore from the BSS, the woman shall, on the discretion of the attending physician, be referred for invasive procedure – amniocentesisorchorionic villus sampling. Usually, when the risk score is between 1:100 and 1:1000 additionalLate BSS is discussed orultrasound screening for structural fetal defectsin 15-19 weeks of pregnancy.

Late biochemical serum screening

It is performed in the period between the 15 and the 20 weeks of pregnancy and gives assessment of the risk with regard to three major groups of congenital fetal abnormalities: Down’s, Patau’s, and Edward’s syndromes and several other chromosomal abnormalities (Trisomy 18, 13), neural tube defects (split spine /spina bifida/ and several brain abnormalities), fetal anterior abdominal wall defects.

Due to conventionality of the calculated risk ofBSS, false-positive results are possible, i.e. positive result, after which the possibility of chromosomal abnormality is ruled out by means of diagnostic procedure, such as amniocentesis or chorionic villus sampling.

The biochemical serum screening (15-20 weeks of pregnancy) for assessing the risk of Trisomy 13, 18, and 21 is a test that is suitable for women under the age of 36. For women above 36, screening or diagnostic test of higher sensitivity are recommended, because the risk of chromosomal abnormalities increases with age.

Early ultrasound screening for congenital fetal defects

It is performed in the period between the 11 and the 14 weeks of pregnancy. The ultrasonography in such an early stage of the fetal development, however, does not furnish sufficient information, as compared to the classical screening in the second trimester (15-21 weeks of pregnancy). The overall detection rate for fetal abnormalities of the first trimester ultrasonography is about 44% as compared to 74% of the later screening. Major abnormalities of the skull shape, of the abdominal wall and of the excretory system, as well as of the navel cord and the placenta, can be detected with relative success at 10-11 weeks.The confirmation of other abnormalities, such as split spine, diaphragmatic hernia or heart defect, however, is very difficult before the 13thweek of pregnancy. Therefore, the routine first trimester ultrasound screening cannot be widely used for detection of spinal cord and heart defects in the general population.

The measurement for increased width of the fetal translucent area (the area between the skin and the neck muscles of the foetus), carried out between 11 and 14 weeks of gestation proves to be a highly informative ultrasound marker for detecting Down’s syndrome in women above the age of 35.

Amniocentesis (AC)

This is a medical procedure during which the physician inserts a needle in the mother’s womb. A small amount of amniotic fluid is extracted (the fluid surrounding the baby) for analysis. AC can detect over 150 diseases, mainly chromosomal and monogenic metabolic defects. Between 12 and 14 weeks of pregnancy can be carried out the so-called early AC, which is technically more difficult and is associated with higher risk of fetal injury. The procedure is usually done when a woman is between 16 and 18 weeks pregnant (late AC) and is associated with miscarriage risk of about 1%. It can detect over 150 diseases, mainly chromosomal and monogenic metabolic defects.

0 %


formiscarriageresulting from amniocentesis.
In Bulgaria this would mean the loss of about 15 to 20 desired pregnanciesannually.

Chorionic villus sampling (CVS)

This medical procedure is related to sampling of a small tissue amount of the exterior wall of the placenta. This tissue can then be tested for chromosomal abnormalities. It is an invasive diagnostic method associated with higher miscarriage risk (about 3-5%), and is carried out in the first trimester (at 9-12 weeks of pregnancy) predominantly in pregnancies at higher risk of genetic disorders (e.g. monogenic defects, family history of a chromosomal abnormality).

Comparative analysis: Biochemical screeningandPrenaTest™

Sensitivity 90% 60-80% 90-92% 99%
False positive results 5% 5% 2% 0.2%
Unsuccessful <1% <1% <1% 0.5%
Week of pregnancy 11-13 г.с. 15-19 г.с. 15-20 г.с. ≥9 седмица