title: Should spontaneous and medically indicated preterm births be separated for studying aetiology?
abstract: An increasing proportion of preterm births result from medical interventions, and the practice of aggregating all preterm births vs. splitting into spontaneous and medically indicated preterm births is inconsistent. While mechanistic and clinical arguments can be offered for either approach, we empirically evaluated the predictiveness of a range of risk factors for preterm birth in the Pregnancy, Infection, and Nutrition Study. Most influences were shared across the two subsets - African-American ethnicity, advancing age, delivery at a university medical centre, prior preterm birth and smoking. Medically indicated preterm births appeared to be associated with intensity of medical care, higher in the university medical centre and lower for the poorest women. Body mass index was positively associated with medically indicated preterm birth and inversely with spontaneous preterm birth. Given the complexity of the aetiological pathways, both aggregation and disaggregation are well justified and should be included in studies of the causes of preterm birth.
authors.affiliation: Carolina Population Center, University of North Carolina, Chapel Hill, NC 27599-7435, USA. david_savitz@unc.edu
authors.forename: David A
authors.initials: DA
authors.lastname: Savitz
authors.forename: Nancy
authors.initials: N
authors.lastname: Dole
authors.forename: Amy H
authors.initials: AH
authors.lastname: Herring
authors.forename: Diane
authors.initials: D
authors.lastname: Kaczor
authors.forename: June
authors.initials: J
authors.lastname: Murphy
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Siega-Riz
authors.forename: John M
authors.initials: JM
authors.lastname: Thorp
authors.forename: Thaddeus L
authors.initials: TL
authors.lastname: MacDonald
mesh_terms: D000328:Adult; D001741:Black or African American; D015992:Body Mass Index; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D016017:Odds Ratio; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious; D047928:Premature Birth / Q000209:etiology*; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects; D012959:Socioeconomic Factors; D016585:Vaginosis, Bacterial / Q000150:complications