[Ultrasound screening at 18-20 weeks.].

Ultrasound screening at 18-20 weeks gestation is widely recognized as an integral part of modern antenatal care. It was set up in Iceland between 1984 and 1986 and has become steadily more advanced. The time for this basic dating and fetal assessment scan was selected in accordance with current medical knowledge, based on several cohort studies, later supplemented by results from randomized trials. Icelandic reference standards were established and the suitability of mostly Scandinavian fetal assessment methods for the Icelandic population was evaluated. Gestational age assessment and placental localisation, along with a thoroughly performed evaluation to ascertain normal fetal anatomy, were conducted systematically. Icelandic guidelines and educational standards for conducting ultrasound were published. As most deviations from the normal, including major anomalies, are found in those not perceived to be at risk, a screening approach was necessary. Better dating of pregnancies and prenatal diagnosis allowing either termination of pregnancy in case of severe fetal anomaly or preparation for correct handling of the neonate at birth, have had a major impact on obstetric practice. Most lethal or seriously handicapped fetuses are detected. The screening scan has become a universally accepted and appreciated part of antenatal care in Iceland.