In the test, lungs that float in water are thought to have been aerated, while those that sink are presumed to indicate an absence of air.
[4] In a 1997 paper, J.J. Moar emphasises the risk of misdiagnosing live birth, writing that the "majority of new born infants seen at autopsy show signs of varying degrees of decomposition, as they are often found in garbage, wrapped in newspaper or plastic bags, or lying in an open field.
Even microscopic putrefaction can cause unexpanded lungs to float, when gas formation may not be macroscopically apparent.
Naturally, any attempts at resuscitation may partially expand the lungs of a new born infant, leading to further difficulty in establishing live birth.
[8] The application of the lung float test to determine breathing and live birth has many spurious medico-legal considerations.