The right time to get a fetal echo has come down to now 18-20 weeks. There is significant advantage to the earlier timing including better imaging. This obviously has been possible by advances made in technology. Additionally, in case a very major abnormality is picked up possibility of termination before 20 weeks is also available.
Though most lesions can be picked up at this stage of pregnancy but a few may not be:
1. Valve Lesions: typically, the valve lesions especially valve blockages (called stenosis) start as a mild problem at 20-24 weeks. They may be so mild; they may not be picked up. And therefore a repeat assessment at 28 weeks or after birth may confirm these diagnoses. Conditions included in this subset include Pulmonary Valve Stenosis and Aortic Valve Stenosis.
2. Coarctation of Aorta: This is blockage of the main tube taking blood into the lower half of the body. This lesion starts at 28 weeks or sometimes maybe earlier. It gradually progresses beyond 28 weeks and typically can be suspected any time beyond that.
3. Cardiac Conditions which show up only indirectly: there are a few lesions which cannot be diagnosed by direct visualisation but by its indirect effects: Aorto Pulmonary Window, Aorto Pulmonary Collaterals, Coronary Cameral Fistula.