title: Birth order and postpartum psychiatric disorders.
abstract: OBJECTIVE
  Primiparity is a well-established and significant risk factor for postpartum psychosis and especially bipolar affective disorders. However, no studies have, to our knowledge, quantified the risk of psychiatric disorders after the first, second, or subsequent births. The overall aim of the present study was to study the risk of first-time psychiatric episodes requiring inpatient treatment after the birth of the first, second, or third child.
  
  
  METHODS
  A cohort comprising 750,127 women was defined using information from Danish population registries. Women were followed individually from the date of birth of their first, second, or third child through the following 12 months over the period 1970-2011. The outcome of interest was defined as first-time admissions to a psychiatric hospital with any type of psychiatric disorder.
  
  
  RESULTS
  Women who had a first psychiatric episode which required inpatient treatment after their first (n = 1,327), second (n = 735), or third (n = 238) delivery were included. The highest risk was found in primiparous mothers 10-19 days postpartum [relative risk (RR) = 8.65; 95% confidence interval (CI): 6.89-10.85]. After the second birth, the highest risk was at 60-89 days postpartum (RR = 2.01; 95% CI: 1.52-2.65), and there was no increased risk after the third birth. The effect of primiparity was strongest for bipolar disorders.
  
  
  CONCLUSIONS
  Primiparity is a significant risk factor for experiencing a first-time episode with a psychiatric disorder, especially bipolar disorders. A second birth was associated with a smaller risk, and there was no increased risk after the third birth. The risk of postpartum episodes after the second delivery increased with increasing inter-pregnancy intervals, a result which warrants further investigation.
authors.affiliation: iPSYCH, National Center for Register-Based Research, Department of Economics and Business, School of Business and Social Sciences, Aarhus University, Aarhus, Denmark.
authors.forename: Trine
authors.initials: T
authors.lastname: Munk-Olsen
authors.forename: Ian
authors.initials: I
authors.lastname: Jones
authors.forename: Thomas Munk
authors.initials: TM
authors.lastname: Laursen
mesh_terms: D000328:Adult; D001722:Birth Order / Q000523:psychology; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D001523:Mental Disorders / Q000175:diagnosis / Q000453:epidemiology*; D008875:Middle Aged; D049590:Postpartum Period; D011247:Pregnancy; D011336:Probability; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012307:Risk Factors; D055815:Young Adult
keywords: bipolar affective disorders; birth spacing; epidemiology; postpartum psychiatric disorders