ABSTRACT
The introduction of high resolution ultrasound to routine obstetric practice has revolutionized prenatal diagnosis. Although anomaly scans in the mid-trimester are still not universally offered in the United Kingdom, the vast majority of obstetric units do provide a scan between 18 and 22 weeks when fetal anatomy is examined. The Royal College of Obstetricians and Gynaecologists first published guidelines for routine ultrasound in pregnancy including anomaly scans in 1997, and these were updated in 2000 (1,2). The central nervous system, one of the main organ systems to be examined, is the site of the first fetal abnormalities diagnosed by ultrasound: anencephaly and spina bifida (3,4).
