Reply to Keelan and Payne: Microbiota-related pathways for preterm birth

We thank Keelan and Payne (1) for their interest in our work (2). Their letter emphasizes intrauterine infection as a potential mechanistic link between the vaginal microbiota and preterm birth. Although we share their view of ascending infection as a possible mechanism, we don’t consider it to be the only possible one. For this and other reasons we discuss below, we are hesitant to adopt the view—which we believe would risk introducing investigator biases—that documented intra-amniotic infection is a necessary accompanying condition for establishing a role of the microbiota in preterm birth.