Down syndrome (DS) is the most common chromosome anomaly among live born infants and is associated with intellectual disability and typical clinical features. Furthermore, DS is associated with other morbidities, like cardiac and gastrointestinal defects and thyroid disorders. DS is caused by the presence of a complete extra chromosome 21 (trisomy 21), partial trisomy, translocation or mosaicism of chromosome 21. In recent decades, the life expectancy of children with DS has improved greatly in particular due to early surgical treatment of congenital heart diseases and anomalies of the gastrointestinal tract. Over the past years, various prenatal aneuploidy screening methods have been developed. These screening methods are aimed at enabling pregnant women to obtain information about the health of their unborn child in order to prepare for the birth of a child with a disorder or to terminate the pregnancy in the case of an abnormal test-result. The non-invasive prenatal test (NIPT) is the latest development and is used to examine the pregnant woman’s blood for aneuploidies, including DS, in the foetus. The blood of a pregnant woman contains a small amount of hereditary material (DNA) from the placenta. This DNA is almost always the same as the DNA of the child. The NIPT is more accurate than previous prenatal tests, like the first-trimester combined test (FCT), to detect DS. In case of an abnormal result of the NIPT, invasive diagnostic tests with amniocentesis or chorionic villus sampling are necessary to confirm the result. Both invasive tests have a very small miscarriage risk. Before 2007, there was no formal prenatal aneuploidy screening programme in the Netherlands, although pilot studies were performed and some tests were locally available. A national programme started in 2007 consisting of all pregnant women receiving information about FCT in the first trimester and offering a structural anomaly scan in the second trimester. A risk higher than 1:200 with FCT or abnormal ultrasound findings later in ...