Early fetal anomaly scanning in a population at increased risk of abnormalities.

Objectives To determine the effectiveness of early fetal anomaly scanning in a population at risk of fetal anomalies. Design A prospective study in a tertiary center of 101 consecutive fetuses at risk of congenital anomalies at 11-14 weeks of gestation. Results The principal (93/101=92%) reason for referral was having a previously affected infant. Nine (9/101=9%) fetuses were shown to have structural anomalies at the 11-14-week scan. In five of nine structurally affected fetuses, the nature of the anomalies was similar to that established in a previously affected pregnancy, four of which had a recurrence of an autosomal recessive syndrome. In two fetuses with a normal 11-14-week scan, anomalies were detected at the 18-21-week (arthrogryposis) or 30-week (cardiomyopathy) scans.\ Conclusions The majority of fetal anomalies can be diagnosed in the late first/early second trimesters of pregnancy. This will be of particular advantage to those women who are at high risk of having affected offspring. However, as fetal anomalies may present at varying gestational ages, the standard 18-21-week scan cannot be abandoned. The effectiveness of the early pregnancy scan depends on the natural history of anomalies (gestational age at onset) and the variable phenotypic expression of anomalies/syndromes.