From The Lancet:(free registration required)
Treatment of asymptomatic abnormal vaginal flora and bacterial vaginosis with oral clindamycin early in the second trimester significantly reduces the rate of late miscarriage and spontaneous preterm birth in a general obstetric population.
Lancet 2003; 361: 983-88
? so should we start to screen at 18 weeks for BV? I'm not yet convinced.