title: The effect of maternal age on adverse birth outcomes: does parity matter?
abstract: OBJECTIVE
  To examine the effect of parity on the association between older maternal age and adverse birth outcomes, specifically stillbirth, neonatal death, preterm birth, small for gestational age, and neonatal intensive care unit admission.
  
  
  METHODS
  We conducted a retrospective cohort study of singleton births in British Columbia between 1999 and 2004. In the cohort, 69 023 women were aged 20 to 29, 25 058 were aged 35 to 39, and 4816 were aged 40 and over. Perinatal risk factors, obstetric history, and birth outcomes were abstracted from the British Columbia Perinatal Database Registry. Logistic regression was used to calculate adjusted odds ratios (aOR) and 95% confidence intervals for adverse outcomes in the two older age groups compared with the young control subjects.
  
  
  RESULTS
  Compared with younger control subjects, women aged 35 to 39 years had an aOR of stillbirth of 1.5 (95% CI 1.2 to 1.9) and women aged >or= 40 years also had an aOR of 1.5 (95% CI 1.0 to 2.4). The aOR for NICU admission was 1.2 (95% CI 1.0 to 1.3) in women aged 35 to 39 years and 1.4 (95% CI 1.1 to 17) in women aged >or= 40 years compared with younger control subjects. The risk of preterm birth and SGA differed by parity. The aOR for preterm birth compared with younger primiparas was 1.5 (95% CI 1.4 to 1.7) for women aged 35 to 39 years and 1.6 (95% CI 1.3 to 2.0) for women aged >or= 40 years. In multiparas the aOR for preterm birth was 1.1 (95% CI 1.1 to 1.2) in women aged 35 to 39 and 1.3 (95% CI 1.1 to 1.5) in women >or= 40 years. The aOR for SGA in primiparas was 1.2 (95% CI 1.1 to 1.4) for women aged 35 to 39 and 1.4 (95% CI 1.1 to 1.7) for women aged >or= 40 years. The risk of neonatal death was not significantly different between groups.
  
  
  CONCLUSIONS
  Older women were at elevated risk of stillbirth, preterm birth, and NICU admission regardless of parity. Parity modified the effect of maternal age on preterm birth and SGA. Older primiparas were at elevated risk for SGA, but no association between age and SGA was found in multiparas. Older primiparas were at higher risk of preterm birth than older multiparas compared with younger women.
authors.affiliation: Department of Obstetrics and Gynaecology, University of British Columbia, Vancouver BC; Child and Family Research Institute, Vancouver BC.
authors.forename: Sarka
authors.initials: S
authors.lastname: Lisonkova
authors.affiliation: Child and Family Research Institute, Vancouver BC; School of Population and Public Health, University of British Columbia, Vancouver BC.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Janssen
authors.affiliation: School of Population and Public Health, University of British Columbia, Vancouver BC.
authors.forename: Sam B
authors.initials: SB
authors.lastname: Sheps
authors.affiliation: Department of Paediatrics, University of Toronto, Toronto ON.
authors.forename: Shoo K
authors.initials: SK
authors.lastname: Lee
authors.affiliation: Department of Obstetrics and Gynaecology, University of British Columbia, Vancouver BC.
authors.forename: Leanne
authors.initials: L
authors.lastname: Dahlgren
mesh_terms: D000328:Adult; D001955:British Columbia; D016022:Case-Control Studies; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007363:Intensive Care Units, Neonatal / Q000706:statistics & numerical data*; D008423:Maternal Age; D010298:Parity; D011247:Pregnancy; D047928:Premature Birth; D012189:Retrospective Studies; D050497:Stillbirth / Q000453:epidemiology*