The cause of postmortem fetal extrusion is not completely understood, as the event is neither predictable nor replicable under experimental conditions. Evidence has accumulated opportunistically and direct observation is serendipitous. While it is possible that more than one cause can produce the same result, there is an accepted hypothesis, based on established research in the fields of biochemistry and forensic taphonomy, and further supported by observational research, that accounts for the taphonomic mechanisms that would result in the most often encountered cases of postmortem extrusion of a non-viable fetus. Typically, as a dead body decomposes, body tissues become depleted of oxygen and the body begins to putrefy; anaerobic bacteria in the gastrointestinal tract proliferate and as a result of increased metabolic activity, release gases such as carbon dioxide, methane, and hydrogen sulfide. These bacteria secrete exoenzymes to break down body cells and proteins for ingestion which thus weakens organ tissues. Increasing pressure forces the diffusion of excessive gases into the weakened tissues where they enter the circulatory system and spread to other parts of the body, causing both torso and limbs to become bloated. These decompositional processes weaken the structural integrity of organs by separating necrotizing tissue layers. Bloating usually begins from two to five days after death, depending on external temperature, humidity, and other environmental conditions. As the volume of gas increases, the pressure begins to force various body fluids to exude from all natural orifices. It is at this point during the decomposition of a pregnant body that amniotic membranes become stretched and separated, and intra-abdominal gas pressure may force the eversion and prolapse of the uterus, which would result in the expulsion of the fetus through the vaginal canal. It has been observed that the bodies of multiparous women are more likely to spontaneously expel the fetus during decomposition than those who died during their first pregnancy, because of the more elastic nature of the cervix.
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