Since January 2007, a nationwide prenatal screening program has been implemented in the Netherlands. The prenatal screening program includes screening for Down-, Edwards-, and Patau syndrome (via NIPT or combined test), and screening for structural anomalies via an anomaly scan around 20 weeks gestation. When the mother has an increased risk, either detected through a screening test or based on family or medical history, prenatal diagnosis is offered through amniocentesis or chorion villus biopsy for genetic aberrations or an advanced ultrasound for structural anomalies. We investigate the sensitivity of the prenatal screening to detect congenital anomalies and which factors can modify this. We also study if the changes in prenatal screening have effect on the timing of detection of congenital anomalies or on the outcome of pregnancy.