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Invasive prenatal tests allow to estimate the risk of birth defects in the fetus. Although the name "invasive" sounds scary, the facts are that the risk of complications from invasive prenatal testing is low and that it is almost 100% effective. What are the indications for invasive prenatal testing, what are the types of these tests and what birth defects can be detected with invasive prenatal testing?

Invasive prenatal testsare performed in order to confirm or exclude a genetic defect of the fetus with almost 100% effectiveness (as the accuracy of these tests is estimated at 99.9%). However, not every one - invasive prenatal tests are performed only for the most common defects and diseases, including:

  • Edwards syndrome
  • Down syndrome
  • Turner syndrome
  • Patau band
  • cystic fibrosis
  • Duchenne muscular dystrophy
  • spinal muscular atrophy
  • Di George's band.

Invasive prenatal tests involve the doctor puncturing the abdomen with a needle and taking a specific type of biological material for examination - e.g. cells or placental tissue. The examination is performed under ultrasound control - the specialist therefore sees the fetus on the screen and maneuvers the needle so as not to touch the baby.

No cells are taken from the child for analysis. The puncture is minimal so it cannot cause a hemorrhage. After the examination, the expectant mother remains under the doctor's care for some time - if she feels unwell, she will receive help quickly.

Prenatal invasive tests are not obligatory, and since each of these tests carries a small risk of miscarriage, the expectant mother must sign a consent form before performing them.

Prenatal invasive tests - indications

The basis for prenatal invasive tests is a higher than usual risk of a birth defect or genetic disease of the fetus. This risk is estimated by the doctor (and he is the one who issues a referral for invasive prenatal examination). When can a doctor issue a referral?

The indications for invasive prenatal examinations are:

  • age of the expectant mother - over 35
  • positive double or triple test
  • abnormal screening ultrasound result,performed between 11 and 14 weeks of pregnancy
  • central nervous system defect in the fetus
  • having a child with a past metabolic disease or birth defect
  • fetal chromosomal abnormalities or sex chromosome aberrations in previous pregnancies
  • chromosomal defects in parents.

Prenatal invasive tests - trophoblast biopsy (chorionic villus sampling)

Chorionic villus sampling is performed between 11 and 14 weeks of pregnancy. It consists in collecting a fragment of the chorion (i.e. the outer fetal membrane) under ultrasound control - it is done either through the abdominal wall or through the vagina (then a special catheter is inserted through the cervix directly into the uterus. The test result is obtained after a few days.

Chorionic villus sampling allows to detect or exclude gene mutations (and diagnose, among others, cystic fibrosis or Duchenne muscular dystrophy), as well as chromosomal aberrations, e.g. trisomy (diagnostics for Down's, Edwards, Patau's syndromes). The risk of miscarriage in the case of a trophoblast biopsy is approx. 1%.

Prenatal invasive tests - cordocentesis

Cordocentesis is a test that can be carried out from the 18th week of pregnancy (usually at 19-20 weeks). Under local anesthesia, the doctor inserts blood through the abdominal wall into the umbilical cord and takes blood from the umbilical cord loop. The examination takes several minutes, but then you have to stay under medical care for several hours.

You have to wait about 7 days for the results. The analysis of the blood of the fetus obtained thanks to cordocentesis can give a lot of information - it will allow, for example, to determine the karyotype (set of chromosomes) and DNA and determine whether the child has a genetic disease. If there is a risk of a serological conflict, the fetal morphology and blood group as well as the number of antibodies in the mother's blood that destroy the red cells of the fetus are examined - if there are many of them, blood transfusion to the fetus is possible while still in the womb.

Cordocentesis is the most difficult prenatal test - and the most risky: it is associated with twice the risk of complications (e.g. miscarriage) than other prenatal tests.

Prenatal invasive tests - amniocentesis

Amniocentesis is performed after the 14th week of pregnancy - usually between the 16th and 19th week. After local anesthesia, the doctor punctures the abdominal wall and the fetal bladder with a needle. She takes about 15 ml of amniotic fluid, i.e. amniotic fluid, with a syringe. There are fetal cells from the exfoliating skin, genitourinary and digestive systems.

On a special, artificial medium, they are cultured in the laboratory, and after the cells are multiplied - the kit is testeda child's chromosomes, i.e. its so-called karyotype. You usually have to wait a month for the test result. It only takes a few minutes to collect the amniotic fluid. Amniocentesis is associated with 0.5-1% of risk of miscarriage.

Amniocentesis allows the detection of almost 200 hereditary diseases, including Down syndrome, Edwards syndrome, haemophilia, as well as Duchenne muscular dystrophy, spinal muscular atrophy, Di George syndrome. The risk of miscarriage or premature birth due to amniocentesis is 0.5-1%.

Pregnancy tests - which are mandatory?

  • Patau syndrome: causes and symptoms. What is the treatment of children with trisomy of chromosome 13?
  • Marfan's syndrome: causes, symptoms, treatment
  • Fabry disease: causes, inheritance, symptoms and treatment
  • Edwards syndrome - causes, symptoms, treatment
  • Down's syndrome - causes, course, diagnosis
  • Anencephaly (anencephaly) - neural tube defect
  • Turner syndrome: causes, symptoms, effects, treatment

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Pregnant examinations