Does the use of antibiotics for bacterial vaginosis during pregnancy reduce the risk of preterm birth?

Bacterial vaginosis (BV) is an inflammatory disease that is defined as a vaginal microbiome that is not dominated by Lactobacilli.  This abnormal vaginal flora is associated with preterm birth and miscarriage.  A recent study showed that women’s vaginal microbiomes shift frequently during pregnancy, but that the amount of time spent with a flora not dominated by Lactobacillus was associated with the length of the pregnancy, i.e. the less time spent with Lactobacillus the shorter the pregnancy.  Considering these studies, doctors may want to begin screening the vaginal microbiome during pregnancy, and treating BV (which is currently done through antibiotics).  Strategies such as that one have not yet been rigorously studied, so their efficacy is still unknown.  Last week a study out of Japan performed a study that showed little improvement in preterm birth risk by monitoring and treating BV during pregnancy.  The results were published in Nature Scientific Reports.

The researchers measured the microbiomes of 1,735 pregnant women and split them into two groups.  Women in the intervention group that had BV were given antibiotics, whereas women in the control group, whether they had BV or not, proceeded as normal through their pregnancy.  Women in both groups had their vaginal microbiomes sampled at various time points throughout the pregnancy. The first group would have their BV status verified, and placed on antibiotics. In both groups, approximately 10% of the women had preterm birth at around 30 weeks gestational age.  There was no significant difference in these rates between the two groups, meaning that administration of antibiotics did not appear to prevent preterm birth.  Even though the antibiotics did not prevent preterm birth, the researchers noted that regardless of group, women who entered preterm birth did have abnormal vaginal flora compared to women who went full term, supporting the notion that BV is highly correlated with preterm birth.  They noted that many of the women who entered preterm labor did not have BV at the initial time of screening, but acquired BV at some point during pregnancy. 

This paper supports the idea that BV may cause preterm birth, however it cannot recommend universal screening for BV in pregnant women for two reasons.  First, the antibiotics did not appear to affect the rates of preterm birth, and second many of the women who had preterm birth only had abnormal flora after initial screening.  Perhaps a better strategy would be to constantly monitor BV status throughout pregnancy.  In addition, there will soon be healthier and more effective methods to treat BV than antibiotics, which are only shown to have a transient effect on BV and disrupt the rest of the microbiome.

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