Is there a bacteria that cause nec or is it something that a mom might do during the pregnancy?

Prematurity: There is no definitive cause of nec known, however it is seen most often in premature babies. Many suspect it has to do with an immature intestinal system, an alteration in blood flow and milk feedings. The bacteria pseudomonas aeruginosa is often implicated in premature babies.

Partially: Cocaine use during pregnancy can increase the risk of nec. The exact cause of nec is not really known however an association between an injury to the lining of the intestine and bacterial overgrowth is suspected.

Unknown: The exact cause of nec is unknown. Nec occurs most commonly in babies born early (premature) and after they have started feeding. There are certain risk factors thought to be associated with nec: birth trauma/hypoxia, exposure to Cocaine or other vasoconstrictors, infection/sepsis, etc.