A healthy vaginal microbiome maintains a level of acidity that keeps troublemaking microbes at bay. When the community becomes unbalanced, vaginosis can result, with devastating consequences. In a study of urban women in Philadelphia, vaginosis in the first trimester more than doubled the risk of spontaneous pregnancy loss. Vaginosis “doesn’t get the attention it deserves, because it’s not a sexy STD,” says Deborah Nelson a professor of public health at Temple, who led the study.