title: Effect of age, parity, and smoking on pregnancy outcome: a population-based study.
abstract: OBJECTIVE
  The purpose of our study was to investigate the combined interactive effects of maternal age, parity, and smoking on pregnancy outcome.
  
  
  METHODS
  This was a population-based Swedish study (n = 538,829).
  
  
  RESULTS
  Multiple logistic regression analysis showed that the smoking-related effect on the relative increase in the odds ratio of low birth weight and preterm delivery was significantly greater among multiparous patients than nulliparous; among multiparas, smoking increased the odds ratios for low birth weight and preterm delivery by 2.4 and 1.6; the corresponding relative increases in the odds ratios among nulliparas were 1.7 and 1.1, respectively. With advancing maternal age there was a smoking-related relative increase in the odds ratios for small-for-gestational-age births. Moreover, the age effect on the relative increase of low birth weight, preterm delivery, and small-for-gestational-age births was greater among nulliparas than multiparas.
  
  
  CONCLUSIONS
  Older smokers are at an especially high risk for small-for-gestational-age births, and parous smokers are at an especially high risk for low birth weight and preterm delivery.
authors.affiliation: Division of Epidemiology, Statistics and Preventive Research, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
authors.forename: S
authors.initials: S
authors.lastname: Cnattingius
authors.forename: M R
authors.initials: MR
authors.lastname: Forman
authors.forename: H W
authors.initials: HW
authors.lastname: Berendes
authors.forename: B I
authors.initials: BI
authors.lastname: Graubard
authors.forename: L
authors.initials: L
authors.lastname: Isotalo
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007226:Infant Mortality; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D008423:Maternal Age; D016017:Odds Ratio; D010298:Parity / Q000502:physiology*; D011247:Pregnancy; D011256:Pregnancy Outcome; D012044:Regression Analysis; D012907:Smoking / Q000009:adverse effects*; D013548:Sweden