In the Netherlands, all pregnant women are offered prenatal screening for Down, Edwards and Patau syndrome (trisomy 21, trisomy 18 and trisomy 13) and for structural anomalies. Currently, the prenatal screening program includes screening for common trisomy’s through the Non-Invasive Prenatal Test (NIPT) from 10 weeks gestation and screening for structural anomalies through an anomaly scan around 13 and 20 weeks of gestation.
This chapter presents uptake of prenatal screening tests and pregnancy outcomes from 2010-2024 for Down, Edwards and Patau syndrome and selected structural anomalies. During this period several changes occurred in the prenatal screening program.
We present trends in prenatal screening and diagnosis using time periods related to these changes in the prenatal screening program.
The prenatal screening program is monitored annually by the regional centers for prenatal screening. The monitoring report over 2024 (Professionalsmonitor 2024, Prenatale screening; de NIPT en structureel echoscopisch onderzoek) and report from previous years can be found at the website of the RIVM.
In 2024 in Northeast Netherlands (exceeding the Eurocat NNL region), screening for Down, Edwards and Patau syndrome was performed in 16,186 pregnancies through NIPT corresponding with an uptake of 68.5%. NIPT resulted in 0.52% in a positive result (i.e. indication that fetus is affected with Down, Edwards or Patau syndrome). Since the introduction of the NIPT as second-tier screening test in 2014, the uptake for screening for Down, Edwards and Patau syndrome increased gradually in the Northeastern region, from 21% in 2015 to 68.5% in 2024 (Figure 1).
The 20 weeks anomaly scan was performed in 20,466 pregnancies (uptake of 87.9%). A structural anomaly was suspected in 4.1% of pregnancies. The 13 weeks anomaly scan was performed in 18,218 pregnancies (uptake of 78.4%). The uptake of the 20 weeks anomaly scan has been constant over the last eight years.
Uptake of the CT/NIPT screening test
In 2010-2024 Eurocat NNL registered 785 cases with either Down (n = 526), Edwards (n = 190) or Patau (n = 69) syndrome. Total prevalence in this period was 22.4, 8.1 and 2.9 per 10,000 births respectively. Time trends for the last 10 years are reported in chapter 6 of the Monitor.
In the same period, 71.5% of the 520 cases with Down syndrome and information available on prenatal detection were prenatally diagnosed. For Edwards (n = 189) and Patau (n = 68) syndrome, 96.3% and 94.1% were prenatally diagnosed respectively. Missing data on time of diagnosis was scarce (n = 8).
Looking at the different time periods related to the changes in the prenatal screening program, an increase in proportion of cases with a prenatal diagnosis was seen for Down syndrome. The average proportion of prenatally detected cases increased from 60% in 2010-2013 (before the introduction of NIPT, only CT) to 64% in 2014-2017 (NIPT available as second-tier test, Trident-1) and 81% in 2018-2024 (NIPT available as first screening test). The proportion of prenatally diagnosed cases with Edwards was 91% in 2010-2013, increasing to 99% in 2018-2024. For Patau syndrome this was 94% in 2010-2013 and it remained stable (95% in 2018-2024, Figure 2).
Prenatal detection rate by condition and birth years
For the prenatally diagnosed cases we determined what the first positive prenatal test was: 1) an increased risk at the CT or a positive result for NIPT, 2) abnormal findings at ultrasound (US), or 3) positive result at chorionic villus sampling (CVS) or amniocentesis (note that first positive prenatal test is defined as first prenatal test whether screening procedure or diagnostic test which indicated a possible congenital anomaly or need for further tests). Of the prenatally diagnosed cases with Down syndrome, the most common first positive prenatal test was CT or NIPT. For Edwards and Patau cases, ultrasound was the most common first positive prenatal test (see Figure 3).
Overall, 38% (n = 201) of the Down syndrome cases were live born, 9% (n = 47) resulted in a fetal death and 53% (n = 278) resulted in a termination of pregnancy. For Edwards syndrome, these proportions were 4% (n = 8), 17% (n = 33) and 78% (n = 149) respectively. For Patau syndrome, these proportions were 13% (n = 9), 23% (n = 16) and 64% (n = 44) respectively.
After prenatal diagnosis of Down syndrome, termination of pregnancy occurred in 74% of the cases, fetal death or stillbirth occurred in 7% and in 19% there was a live birth. For Edwards syndrome the proportions were 82% terminations, 15% fetal deaths and stillbirths and 3% live births, for Patau syndrome the proportions were 69% terminations, 19% fetal deaths and stillbirths and 13% live births (Figure 4).
When the CT or NIPT provided a positive test result followed by a prenatal diagnosis, pregnancy termination occurred in 86% of the Down syndrome cases and in 9% the outcome of pregnancy was a live birth (Figure 5). When the ultrasound was the first positive test (an ultrasound finding followed by a prenatal diagnosis), termination of pregnancy occurred in 58% of the Down syndrome cases and in 31% there was a live birth. Pregnancy outcome was therefore related to the type of screening test.
After a positive CT or NIPT followed by prenatal diagnosis of Edwards syndrome, termination of pregnancy occurred in 92% of the cases (Figure 2). When the ultrasound was the first positive test (an ultrasound finding followed by a prenatal diagnosis), termination of pregnancy occurred in 76% of the cases and in 20% the pregnancy ended in a fetal death or stillbirth.
After a positive CT or NIPT, or CVS or amniocentesis, followed by prenatal diagnosis of Patau syndrome, termination of pregnancy occurred in 100% of the cases (Figure 2). When the ultrasound was the first positive test (an ultrasound finding followed by a prenatal diagnosis), termination of pregnancy occurred in 56% of the cases and in 27% the pregnancy ended in a fetal death or stillbirth. It needs to be noted that the number of cases with Patau is very small, explaining these large differences in percentages.
In 2010-2024 Eurocat NNL registered 128 cases with non-genetic abdominal wall defects, 220 cases with non-genetic neural tube defects (NTD), and 522 cases with non-genetic severe heart defects. Total prevalence in this period was 5.8, 10.0, and 23.7 per 10,000 births respectively. Time trends are reported in chapter 6 of the Monitor.
Prenatal diagnosis occurred in 97% (n = 166 of 171 cases with information on timing of diagnosis) of the cases with NTDs and in 92% (n = 83/90) of the cases with an abdominal wall defect. For severe CHD the proportion prenatally diagnosed was 63% (n = 152/241).
For the prenatally diagnosed cases we determined the first positive prenatal ultrasound (defined as the first prenatal ultrasound whether performed as dating scan, screening test, or as a diagnostic test which indicated a possible congenital anomaly or need for further tests) and at what time in pregnancy this ultrasound was performed (until 14 weeks or after 14 weeks).
For abdominal wall defects, 56% of the cases were diagnosed during the ultrasound <14 weeks, and 44% of the cases were diagnosed during the ultrasound >= 14 weeks. For neural tube defects, 63% was diagnosed during the late ultrasound >= 14 weeks. In cases with severe heart defects, almost all (90%) were diagnosed during the late ultrasound >= 14 weeks.
Overall, 38% (n = 116) of the cases with abdominal wall defects were live born, 13% (n = 41) resulted in a fetal death and 49% (n = 151) resulted in a termination of pregnancy. For neural tube defects, these proportions were 15% (n = 65), 4% (n = 17) and 81% (n = 355) respectively. For severe heart defects syndrome, these proportions were 66% (n = 772), 5% (n = 58) and 29% (n = 341) respectively.
After a prenatal diagnosis of abdominal wall defects, the majority of cases were live births (57%). Termination of pregnancy occurred in 36% of the cases after this prenatal diagnosis. After a prenatal diagnosis of neural tube defects, termination of pregnancy occurred in most of the cases (84%). After a prenatal diagnosis of severe heart defects, the majority of cases were live births (59%), and termination of pregnancy occurred in 36% of the cases. (Figure 7).
For all three anomalies, termination of pregnancy occurred more frequently when the detection of the anomaly was early in pregnancy, than when the anomaly was detected in the second trimester of pregnancy or later (Figure 8). This is most likely related to the severity of the anomaly.
