Ultrasound in antenatal diagnosis of structural abnormalities

Ultrasound screening has become an accepted part of antenatal practice despite limited evidence to support it. Although 18–20 weeks is the traditional time to screen for structural abnormalities, a number of abnormalities such as acrania and anterior abdominal wall defects can be detected with confidence as early as 11–14 weeks of gestation. The UK Fetal Anomaly Screening Programme (FASP) leads the creation of national guidelines to standardize the practice in the UK. Structural abnormalities can be isolated, or be associated with an underlying chromosomal abnormality or a genetic syndrome. Whilst parental expectations are high, antenatal ultrasound is a screening test and will have false negatives and positives. Antenatal detection rates are higher in countries with a national screening programme. Although 3D/4D ultrasound can generate an image that the parents can better relate to, the advantages over conventional ultrasound are limited. Fetal MRI plays an important complementary role in assessment of fetal brain abnormalities. Input from multiple specialities may be needed following antenatal detection of structural abnormality. Health professionals should provide appropriate information to the prospective parents but remain non-judgemental with their counselling.