Multiple indicators of maternal infection for women in the tocolytic-eligible group included clinical diagnoses documented in the medical record, individual signs or symptoms of infection as recorded during the admission for delivery up to 24 hours postpartum, culture data, inpatient treatment with anti-infective medications, and placental pathological findings. Copies of all available placental pathological reports were reviewed and coded by one of us (R.W.R.), an expert placental pathologist blinded to case status. Laboratory reports from blood, urine, or placental cultures were reviewed and coded by one of us (R.E.W.), an infectious disease specialist blinded to case status. Bacteria and viruses that commonly cause neonatal sepsis and death were classified as group 1, including group B streptococci, Escherichia coli, Staphylococcus aureus, Neisseria gonorrhoeae, Listeria monocytogenes, Bacteroides fragilis, Pseudomonas aeruginosa, and herpes simplex virus. Classified as group 2 were organisms that are frequent commensals and contaminants but may cause disease and organisms that often cause subclinical disease and are not detected unless expressly sought. Included in group 2 were Mycoplasma hominis, Chlamydia trachomatis, Ureaplasma urealyticum, α or γ streptococci, enterococci, coagulase-negative staphylococci, lactobacilli, Gardnerella vaginalis, Haemophilus species, yeast, anaerobic organisms, and normal/mixed flora.