The answers to your questions
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.
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.
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.
The risk of miscarriage following amniocentesis or CVS is about 1%.
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.
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.
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