Pregnant women with a persistent infection of bacterial vaginosis (BV), a relatively common yet troubling infection resulting from an imbalance of good flora in a woman’s vagina, could be at an increased risk for preterm birth, researchers at the March of Dimes Prematurity Research Center (PRC) at Stanford found in a recent study.
While pregnant women without BV had a 5.7% risk of delivering early in the study, women with BV were at a higher risk of preterm birth, and women with more severe cases of BV, which the researchers termed ‘persistent BV,’ saw their risk increase even more.
The paper, published in the American Journal of Perinatology in May, was led by Stanford Medicine OB-GYN professor and first author Dr. Yair Blumenfeld in collaboration with PRC investigator and senior study author Dr. Gary Shaw. The study analyzed a vast database of pregnancy and drug prescription information belonging to 2.5 million women. Of those, nearly 64,000, or about 2.5%, were presumed to have been treated for a BV infection during pregnancy based on prescriptions for one or two drugs most commonly used for that purpose.
Compared to women without a prescription, meaning no BV (who had a 5.7% risk of preterm birth), women with a BV prescription had a 7.5% risk of preterm birth, an increased risk of about 32%.
The highest risk, however, was for women with persistent BV, defined as needing three or more medication prescriptions to treat, or having the condition in both the first and second trimester. Those women saw their risk of preterm birth increase by 48% and 66%, respectively, which in absolute terms meant that their risk for preterm birth jumped to 8.4% and 9.5%, respectively.
While the results still need to be validated in other, more diverse cohorts with more conclusive data about BV diagnosis and treatment (instead of just prescription data involved in this study), the research presents a solid association between persistent BV infection and preterm birth, said Dr. Blumenfeld.
He added that the team’s work to quantify the number of women presumed to be treated with BV during pregnancy, as well as to pinpoint when in the pregnancy they were treated, had not been done before.
“First, the data allowed us to assess how often women are presumably treated for BV in pregnancy and the gestational age of treatment. This was novel,” he said. “Second, we were able to assess how often prescriptions were filled more than once and in more than one trimester. Finally, we were able to find an association between those that filled a prescription in more than one trimester or more than once with an increased risk for [preterm birth].”
“Therefore, our conclusion was that women with persistent presumed BV could be at an increased risk for [preterm birth].”
Although BV may have a bad reputation for being the result of sexual activity or douching, both of which can cause BV, the most common cause is changes to the normal bacterial vaginal flora. The unique composition of each woman’s flora is often in flux, influenced by many factors, some of which are still unknown and the topic of inquiry at several March of Dimes PRCs.
But despite its relatively common occurrence, the infection, which can clear on its own without treatment and is most often associated symptomatically with a discharge or odor, can be a precursor to other serious conditions like preterm birth and cervical cancer-linked HPV infections.
The same culprits are at play in all these conditions: too much bad bacteria inside a woman’s vaginal microbiome (made of fungi, bacteria, and viruses) that cause an inflammatory response. In the case of pregnancy, that inflammatory response could trigger labor, said Stanford Medicine OB-GYN professor Dr. Ronald Gibbs, another study author.
“BV is accompanied by increased inflammatory cytokines which could trigger premature uterine activity,” he said, which gives the link observed in the study between persistent BV and preterm birth “biological plausibility.”