title: Do the causes of infertility play a direct role in the aetiology of preterm birth?
abstract: BACKGROUND
  It is well established that singletons born of assisted reproductive technology are at higher risk of preterm birth and other adverse outcomes. What remains unclear is whether the increased risk is attributable to the effects of the treatment alone or whether the underlying causes of infertility also play a role. The aim of this study was to examine whether any of the six categories of causes of infertility were associated with a direct effect on preterm birth using causal mediation analysis.
  
  
  METHODS
  We assembled a hospital-based cohort of births delivered at a large tertiary care hospital in Montreal, Canada between 2001 and 2007. Causes of infertility were ascertained through a clinical database and medical chart abstraction. We employed marginal structural models (MSM) to estimate the controlled direct effect of each cause of infertility on preterm birth compared with couples without the cause under examination.
  
  
  RESULTS
  The final study cohort comprised 18,598 singleton and twin pregnancies, including 1689 in couples with ascertained infertility. MSM results suggested no significant direct effect for any of the six categories of causes. However, power was limited in smaller subgroup analyses, and a possible direct effect for uterine abnormalities (e.g. fibroids and malformations) could not be ruled out.
  
  
  CONCLUSIONS
  In this cohort, most of the increased risk of preterm birth appeared to be explained by maternal characteristics (such as age, body mass index, and education) and by assisted reproduction. If these findings are corroborated, physicians should consider these risks when counselling patients.
authors: Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, Canada.
authors: Carmen
authors: C
authors: Messerlian
authors: Robert W
authors: RW
authors: Platt
authors: Baris
authors: B
authors: Ata
authors: Seang-Lin
authors: SL
authors: Tan
authors: Olga
authors: O
authors: Basso
mesh_terms: D000328:Adult; D002170:Canada; D015331:Cohort Studies; D037001:Directive Counseling; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007246:Infertility / Q000150:complications* / Q000503:physiopathology / Q000628:therapy; D011247:Pregnancy; D011256:Pregnancy Outcome; D047928:Premature Birth / Q000209:etiology* / Q000517:prevention & control; D027724:Reproductive Techniques, Assisted / Q000009:adverse effects*; D018570:Risk Assessment
keywords: causal mediation analysis; causes of infertility; infertility; marginal structural models; preterm birth