Routine first trimester dating scanning has a number of benefits like
(1) it is more accurate at assessing gestational age than menstrual periods, and therefore reduces the
rates of induction of labour for post-term pregnancies
(2) detects multiple pregnancies early in pregnancy and
(3) can detect some major structural anomalies such as anencephaly.
Nuchal scan or Nuchal translucency (NT) scan: A more detailed, although limited, anomaly scan is incorporated into a nuchal scan or nuchal translucency (NT) scan which helps in determining the basics such as
- the shape of the fetal skull,
- presence of nose, hands and feet and
- presence of stomach and bladder.
Therefore, instigation of Down’s syndrome screening strategies such as the Combined or Integrated test which involve an NT scan are likely to not only increase the detection of aneuploidy but also major structural anomalies and particularly cardiac defects earlier in gestation.
Routine Second Trimester Ultrasound Screening For Fetal Anomalies
In the UK and most of the other countries around the world. there is a policy of routine second trimester ultrasound screening for fetal anomalies .
However, detection of fetal anomalies varies considerably depending on the anomaly being screened for as well as the gestation at screening, the skill of the operator and the quality of the equipment used.
The detection of cardiac anomalies is of particular interest. Early prenatal detection of congenital heart disease (CHD) has increased due to advances in ultrasound resolution and the incorporation of at least a 4-chamber cardiac view in the routine anomaly scan.
