Your guide to health and prenatal genetics
Mother hold baby

Assess your personalised prenatal risks, choose screening tests, and find nearby maternity clinics

What is invasive prenatal diagnostic testing?

If biochemical, ultrasound or modern molecular (NIPT) screening tests show that you have a higher risk of having a baby with particular chromosomal abnormalities (such as trisomic Down, Edwards or Patau syndromes) or particular hereditary conditions, usually you will be offered an invasive diagnostic test to find out with certainty if your baby has the condition. Some women over 35 years also decide to progress directly to invasive prenatal testing. Appropriate genetic counselling is important in all cases.

During invasive prenatal procedures, a fetal material is sampled directly from a womb of the mother and prepared chromosomes or DNA of the fetus is then directly analysed using sophisticated molecular techniques, such as FISH, DNA aneuploidy or chromosomal microarrays analysis (CMA).

There are two main invasive prenatal diagnostic techniques – chorionic villus sampling (CVS) and amniocentesis, which mostly differ in timing and risk to the fetus.





Small pieces of fetal villi (from placenta) are removed by inserting needle through maternal abdomen (transabdominal) or vagina (transcervical) into uterus, guided by ultrasound

Sample (~20 ml) of amniotic fluid is removed by insertion of needle through maternal adbomen into uterus, guided by ultrasound


Placental villi

Amniotic fluid


11-13 weeks

15-20 weeks

Miscarriage risk

0.5-1% or lower* (transabdominal), depends on provider experience; 1-2% (transcervical)

0.5-1% or lower**, decreases with provider experience 

Biochemical AFP testing




Specialist centres

Most obstetric units


  •  Accurate
  •  1st trimester test – earlier results
  •  Accurate
  •  Widely available
  •  Tests for neural tube defects


  •  Availability varies
  •  Does not test for neural tube defects
  •  Increased rate of repeat procedures due to inconclusive results
  •  2nd trimester test
  •  later results

Schematic representation

* - recent data indicates similar risk to amniocentesis in experienced hands

** - recent studies suggest that miscarriage risk maybe lower than 1 in 200 (0.5%) or 1 in 300-400.

Formal indications suggesting prenatal diagnostic testing:

1. Increased risk of aneuploidy:

  • Increased maternal age
  • Abnormal maternal screening (MSS)
  • Abnormal cell free DNA screening
  • Detected fetal ultrasound abnormalities
  • Chromosomal translocation in parents

2. Increased neural tube and ventral wall defects

  • elevated AFP in maternal serum

3. Increased risk of genetic disease (family history or carrier of pathogenic mutation)

4. Maternal request

Current ACOG guidelines recommends invasive prenatal testing for all pregnant women, regardless of age, to obtain a definitive diagnosis of certain birth defects. Therefore, most physicians offer diagnostic testing to all their patients, with or without prior screening and allow a patient decide.