Babies with heart defects may not show symptoms. Pulse oximetry (oxygen saturation check) can aid the diagnosis in some cases. The sensitivity of the test however has been reported as being low detecting only 75% of babies with major CHD and 49% with critical CHD, so with a negative result you could not be completely certain that the baby was free of major or critical CHD (http://www.nhs.uk/news/2011/08August/Pages/pulse-oximetry-newborn-babies-heart-defects.aspx)
Why infer, when you can actually check?
Specialist clinical review and echocardiography remains the gold standard for diagnosis. Investment in fetal cardiac diagnosis and training for sonographers would be a more effective strategy to help identify and manage babies at risk