BV is associated with preterm labor, premature rupture
of the bag
of waters which leads to preterm labor, low-birth weight infant, infection
of the amniotic fluid, placenta and baby during labor, PID (like BeeHappy76 mentioned) and even endometriosis. In fact it is estimated that 15%-20% of all pregnant women have bacterial vaginosis. It is also associated with an increased incidence of miscarriage (in the first-trimester).