Limitations

Some heart abnormalities are not detectable prenatally even with a detailed expert examination. These tend to be minor defects, such as small holes or mild valve abnormalities. Some structure (defect) is part of the normal fetal heart and necessary for survival and may be present during neonatal echocardiography such as PFO, PDA etc. 

In addition, some defects go undiagnosed due to technical limitation such as a very thin structure, unfavorable position of the baby, high abdominal fat content, etc.

Most of the studies have shown the sensitivity of fetal echo only as high as 90%. This means that in 10 % of cases a minor of a major defect can go undiagnosed due to various reasons. In some cases, a diagnosis is made but severity might be under or overstated.

The fetal echocardiogram focuses on the heart so the fetal echocardiographer may not see defects in other parts of the baby.

Having listed a significant number of limitations, the fetal echo helps in diagnosing significant numbers of heart defects and has helped to achieve a favorable outcome. And a fetal echo by an expert always assures better results.