Routine ultrasound scanning for congenital abnormalities

Screening has been defined as "the systematic application or a test or enquiry, to identify individuals at sufficient risk of a specific disorder to benefit from further investigation or direct preventive action, among persons who have not sought medical attention on account of symptoms of that disorder" (Wald, N.J. 1994. J. Med. Screen. 1:76). The purpose of screening is to benefit the individuals being screened. The early detection of abnormalities should not be an end in itself, and the value of a screening approach needs to be determined before it is introduced into practice. Ultrasound as a means of screening for fetal abnormalities has not been adequately assessed even though it is widely used in this way. To assess its value it is helpful to classify abnormalities that can be detected on the basis of the clinical usefulness of doing so. To this end we propose four categories similar to those independently suggested by the Royal College of Obstetricians and Gynaecologists Working Party on Ultrasound Screening for Fetal Abnormalities. Four groups were specified: (A) major abnormalities--death inevitable, (B) abnormalities associated with long-term handicap, (C) abnormalities potentially amenable to intrauterine treatment, and (D) fetal conditions that require immediate postnatal investigation and/or treatment. For each abnormality, the screening detection and false-positives need to be estimated together with the medical and financial costs of screening, particularly those arising from findings of uncertain or little medical consequence that may lead to worry and further unnecessary obstetric intervention.