Risk of spontaneous preterm delivery in a low-risk population: the impact of maternal febrile episodes, urinary tract infection, pneumonia and ear-nose-throat infections

Objective: To assess the associations between maternal infections during pregnancy (i.e. ear-nose-throat infection, pneumonia, urinary tract infection, febrile episodes and influenza-like infection) and spontaneous preterm delivery (SPTD). Study design: Prospective questionnaire data from the Norwegian Mother and Child Cohort (MoBa) study, including more than 100 000 pregnancies and, collected during 1999-2008, were used. Linked data from the Medical Birth Registry of Norway were added. SPTD occurring between gestational weeks 22 + 0 days and 36 + 6 days was the main outcome. Data were analysed in two steps because questionnaires (including information about occurrence of the various infections so far) were completed at different stages of pregnancy. Hazard ratios (HR) were obtained using Cox regression. Results: The SPTD proportion was low in this cohort: 2.9% and 2.7% at the two analysis steps, respectively. After exclusions, 67 310 and 60 689 pregnancies, respectively, remained for the analyses. Ear-nose-throat infections occurring before week 17 were associated with an increased risk of SPTD in the first (HR: 1.27, 95% Cl: 1.08-1.50) and second (HR: 1.26, 95% Cl: 1.04-1.52) step of the analysis, but not if occurring later in pregnancy. None of the other maternal infections were associated with an increased risk of SPTD. Conclusion: In this low-risk population, ear-nose-throat infection in early pregnancy was associated with an increased risk of SPTD. However, infectious morbidity in later pregnancy was not. Thus, the link between maternal infection and preterm delivery may vary in different populations and health care settings. (C) 2011 Elsevier Ireland Ltd. All rights reserved.