Preterm delivery was reduced in pregnant women who had a previous preterm birth and an imbalance of bacteria in the vagina (bacterial vaginosis) during the current pregnancy. There was no reduction in preterm delivery in pregnant women with previous preterm birth without a bacterial imbalance during the current pregnancy (two trials). Postpartum endometritis, or infection of the uterus following birth, was reduced overall (three trials, moderate quality of evidence), as well as in a trial of high-risk women who had a previous preterm birth (one trial, moderate quality of evidence). No reduction in neonatal illness was observed. Outcomes of interest were available in trials with high losses to follow-up. We could not estimate the side effects of antibiotics since side effects were rare; however, antibiotics may still have serious side effects on women and their babies.
There is, therefore, no justification to give antibiotics to all pregnant women during the second or third trimester to prevent adverse infectious effects on pregnancy outcomes.
Authors' conclusions:
Antibiotic prophylaxis did not reduce the risk of preterm prelabour rupture of membranes or preterm delivery (apart from in the subgroup of women with a previous preterm birth who had bacterial vaginosis). Antibiotic prophylaxis given during the second or third trimester of pregnancy reduced the risk of postpartum endometritis, term pregnancy with pre-labour rupture of membranes and gonococcal infection when given routinely to all pregnant women. Substantial bias possibly exists in the review's results because of a high rate of loss to follow-up and the small numbers of studies included in each of our analyses. There is also insufficient evidence on possible harmful effects on the baby. Therefore, we conclude that there is not enough evidence to support the use of routine antibiotics during pregnancy to prevent infectious adverse effects on pregnancy outcomes.