1. Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Maternal and Child Health Research Center, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania
2. Department of Microbiology and Immunology, Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, Maryland
3. Department of Pediatrics, University of Pennsylvania, Perelman School of Medicine, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania