Background. Anomalies of the vaginal flora (bacterial vaginosis, BV) are associated with an increased risk of late abortions and preterm birth. Studies of antibiotic treatment of BV to reduce the risk of prematurity have not found a statistically significant diminution of risk (<= 32 wks: OR=0.49 [0.05-5.1], < 37 wks: OR=0.83 [0.59-1.17]).A partial explanation of these findings is that some of these treatment were administered vaginally, most often during the second or third trimester

Aim: To reduce the frequency of late abortions and very preterm birth by prescribing clindamycin vs placebo to patients diagnosed with BV before 13 weeks.

Patients diagnosed with BV before 13 weeks will be divided into two groups. They will be defined as at low risk when they have no history of spontaneous preterm delivery or late abortion. Women with such histories will be defined as at high risk.

Low risk patients will be asked to participate in a trial with 3 equal parallel groups, comparing two regimes of clindamycin (one or three 4-day treatments of clindamycin 300 mgx2/d) and placebo.

High-risk patients will be asked to participate in a trial with 2 parallel groups to assess the usefulness of repeating antibiotic treatment monthly by comparing the administration of one 4-day treatment of clindamycin (300 mgx2/d) to three 4-day treatments, one month apart.

Inclusion Criteria:

• Nugent score >= 7
• pregnant women < 15 weeks (strictly)
• signed informed consent
• >=18 old
• speaking and understanding French language

Exclusion Criteria:

• metrorrhagias during 7 days before
• birth anticipated in an other area
• clindamycin allergy