The main causes of adverse pregnancy outcome(s) are reported to be maternal infection and placental, fetal, or uterine pathosis. Maternal infection and placental pathosis appear to be the most important causal factors, but each can cause pre-term labour, premature pre-term membrane rupture, or result in medically induced pregnancy interruption. Prominent risk factors for pre-term birth include history of previous pre-term birth, demographic characteristics, periodontal disease, and behavioral factors such as tobacco use.