Impact of the 20-week scan

This thesis presents the results of a number of studies on the efficacy of the 20-week scan in detecting severe congenital anomalies. Data from two of the eight regional centers for prenatal screening was used, located in the Academic Medical Center in Amsterdam and the Academic Medical Center in Groningen, the Netherlands. Overall uptake of the 20-week scan was 93%. During the study 4.3% cases were referred for an advanced diagnostic scan within two weeks after a 20-week scan. More than sixty percent of the selected severe congenital anomalies were diagnosed at the time of the 20-week scan. This overall prenatal detection rate increases to almost 80% taking into account only those cases not diagnosed during the first trimester. Congenital heart defects and cleft lip are most often missed during the 20-week scan. If sonographers who perform dating scans are trained in assessment of the fetal anatomy, the majority of severe congenital anomalies can be diagnosed prior to the 20-week scan (not taking into account those anomalies that manifest later in pregnancy).