Infection in the prediction and antibiotics in the prevention of spontaneous preterm labour and preterm birth.

Preterm birth is the major cause of perinatal mortality and morbidity in the developed world. Infection is a significant cause of spontaneous preterm labour in up to 40% of cases. Women with abnormal genital tract flora diagnosed by bacterial vaginosis on gram stain of vaginal secretions in pregnancy are at increased risk of late miscarriage and preterm birth. The earlier in pregnancy at which spontaneous preterm labour occurs, the more likely this is to be due to a pathological signal or trigger like infection. The earlier in pregnancy at which abnormal genital tract flora is detected, the greater is the risk of a subsequent infective adverse outcome. Even if abnormal genital tract flora in early pregnancy subsequently reverts to normal, there is a greater risk of an adverse outcome when compared to women whose vaginal flora was always normal. It follows that if antibiotics are to be used in pregnancy to treat abnormal genital tract flora, these should be used early in pregnancy before the inflammatory response leading to irreversible tissue damage has occurred. Historically, antibiotic studies have failed because the wrong antibiotics were used in the wrong women too late in pregnancy. Three recent randomized controlled trials have shown that clindamycin used in early pregnancy even in women at low risk of preterm birth can reduce the risk by 40-60%.