The purpose of this FAQ is to provide information on prenatal screening tests, amniocentesis, the risk of miscarriage and adverse events such as Down syndrome and other anomalies that may occur during pregnancy.



Prenatal screening assesses the level of risk in a pregnancy and whether a diagnostic test, such as an amniocentesis in the 15th week or a CVS (placenta) in the 11th week, is needed.

FERTILYS has an that goes far beyond screening for trisomy 21 (Down syndrome). It also includes prediction of maternal conditions such as pre-eclampsia and other adverse events in pregnancy. The detects 96% of trisomy 21 pregnancies with just 2.5% false positives.


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What is an amniocentesis?

Amniocentesis, the most widely used method of prenatal diagnosis, cannot usually be offered before the 15th week. It involves inserting a thin needle into the uterus to withdraw a small amount of the liquid surrounding the fetus, the amniotic fluid. After culture, the chromosomes of the fetal cells (amniocytes) present in the amniotic fluid are analyzed. The results, which are usually available within two to three weeks, will be given to you by your treating physician as soon as they are ready.

Chorionic villus sampling

A chorionic villus sampling (CVS) can sometimes be performed instead of an amniocentesis. It involves taking a sample of cells from the placenta using fine-needle aspiration under ultrasound guidance. Unlike amniocentesis, CVS has the advantage that it can be performed earlier, between the 11th and 15th week. The results are also usually available more quickly, within 5 to 10 days.

What are the risks involved in these tests?

The risk of miscarriage following amniocentesis or CVS is about 1%.

What are your screening options?

There are various types of test that estimate the risk of your fetus having a chromosomal abnormality more accurately than maternal age alone:

  • between the 11th and 14th week (maternal blood markers and nuchal translucency ± other ultrasound markers);
  • Prenatal screening of maternal blood between the 14th and 22nd week with ultrasound dating;
  • Detailed fetal ultrasound at around the 18th to 22nd week.

* It is important to remember that these screening tests only assess a risk or chance. They do not provide a definitive answer and are therefore not diagnostic tests. Amniocentesis is available to all women aged 35 and over and to those considered high risk after screening or genetic counselling. Like CVS, amniocentesis carries a risk of fetal loss.

Results to date

The first trimester prenatal screening program is offered in over 200 centres in 41 countries worldwide. Millions of women have been examined and over 90% of all serious chromosomal abnormalities have been identified.

This program is far superior to prenatal screening based on maternal age alone, which only detects 30% of chromosomal abnormalities. In addition, fetal ultrasound provides important information in multiple pregnancies. There is also increasing evidence that early fetal ultrasounds, performed between the 11th and 14th week, help to identify fetuses with heart defects or genetic syndromes.


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The table below shows the probability of having a baby with Down syndrome based on maternal age alone. The risk that the fetus has a chromosomal abnormality is higher in early pregnancy than at birth as many affected fetuses spontaneously die during pregnancy.

The risk of having a child with Down syndrome based on maternal age alone

Age (years) Risk of trisomy 21 at birth
20 1 in 1526
25 1 in 1351
30 1 in 894
32 1 in 658
34 1 in 445
36 1 in 280
38 1 in 167
40 1 in 96
42 1 in 55
44 1 in 30


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FERTILYS Fertility Centre – Fertility, In Vitro Fertilization, Prenatal Screening