The 'hydrostatic test' (docimasia pulmonum) is performed at autopsy to determine whether a neonate was liveborn. What is the CORRECT interpretation of this test?

• A Lungs that float in water confirm the child was born alive and breathed; this is definitive proof of live birth
• B Floating lungs suggest air entered the lungs (consistent with breathing after birth), but putrefaction can cause false-positive floating ✓
• C Sinking lungs confirm the child was stillborn; this finding is never falsely negative
• D The test measures total lung-to-body weight ratio and is valid up to 7 days post-mortem

Explanation

The hydrostatic (flotation) test: lungs that float in water indicate trapped air from breathing, suggesting the neonate breathed after birth (liveborn). However, it is not an absolute test — putrefaction gases can cause lungs of a stillborn infant to float (false positive). Conversely, atelectasis or early-onset respiratory distress can cause failure to float even in a liveborn infant (false negative). The test should be interpreted alongside other findings. Fragments sinking after squeezing (Wredin's test) increases specificity by releasing trapped decomposition gas.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

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Written and medically reviewed by the StethoPrep medical team.