Final answer:
The most important cause of sepsis in a pregnant woman is a bacterial infection, particularly in the form of puerperal sepsis post-childbirth.
Step-by-step explanation:
The most important cause of sepsis in a pregnant woman is a bacterial infection. In the context of pregnancy, a specific type of sepsis known as puerperal sepsis can occur, which is primarily associated with bacterial organisms infecting the reproductive system after childbirth. This condition was historically called childbed fever or puerperal fever. Further, it is significant to recognize that pregnant women are at a greater risk for certain bacterial infections, such as those caused by Listeria monocytogenes, due to an immune system that is downregulated during pregnancy. The bacteria most commonly associated with puerperal sepsis include Streptococcus spp., Staphylococcus spp., and Escherichia coli among others, which can quickly spread leading to septicemia and death if not promptly treated.