title: The contribution of assisted conception, chorionicity and other risk factors to very low birthweight in a twin cohort.
abstract: OBJECTIVE
  To investigate the contribution of assisted conception (assisted reproductive technology and ovulation induction), chorionicity and selected maternal risk factors for very low birthweight.
  
  
  METHODS
  Retrospective twin cohort study.
  
  
  METHODS
  Staff model Colorado Health Maintenance Organization.
  
  
  METHODS
  Five hundred and sixty-two twin gestations [assisted = 193 (34%); unassisted = 369 (66%)].
  
  
  METHODS
  Data were collected from a perinatal database and medical record review. Data were analysed using univariate and multivariable logistic regression analysis.
  
  
  METHODS
  Very low birthweight.
  
  
  RESULTS
  Women with assisted twin gestation were more likely to be older, nulliparous, non-smokers, married, have a prior history of a miscarriage and a dichorionic placentation. There was no difference in the distribution of low and very low birthweight, discordant growth or preterm delivery between assisted and unassisted twin gestations. Significant risk factors for very low birthweight were: a prior preterm birth (odds ratio, OR, 3.8, 95% confidence interval, CI, 2, 7), monochorionicity (OR 3, 95% CI 2, 4.7), nulliparity (OR 2, 95% CI 1.3, 3), cigarette smoking (OR 1.8, 95% CI 1, 3) and prior miscarriage (OR 1.6, 95% CI 1, 2). Monochorionicity was significantly associated with adverse perinatal outcomes.
  
  
  CONCLUSIONS
  Assisted conception did not play a significant role in the occurrence of very low birthweight in this cohort. A history of preterm birth and a monochorionic twin gestation were the leading risk factors for very low birthweight. Associated risk factors for very low birthweight were nulliparity, cigarette smoking and a prior miscarriage.
authors.affiliation: Clinical Research Unit, Kaiser Permanente, Denver, Colorado, USA.
authors.forename: Anne
authors.initials: A
authors.lastname: Lynch
authors.forename: Robert
authors.initials: R
authors.lastname: McDuffie
authors.forename: Janet
authors.initials: J
authors.lastname: Stephens
authors.forename: James
authors.initials: J
authors.lastname: Murphy
authors.forename: Kenneth
authors.initials: K
authors.lastname: Faber
authors.forename: Miriam
authors.initials: M
authors.lastname: Orleans
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D019102:Infant, Very Low Birth Weight; D016015:Logistic Models; D015999:Multivariate Analysis; D010298:Parity; D011247:Pregnancy; D011272:Pregnancy, Multiple; D027724:Reproductive Techniques, Assisted / Q000009:adverse effects*; D012189:Retrospective Studies; D012307:Risk Factors; D014427:Twins