title: Prospective study of time to pregnancy and adverse birth outcomes.
abstract: OBJECTIVE
  To investigate the association between time to pregnancy (TTP) and adverse birth outcomes.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  A total of 3,521 singletons born to women aged 18-40 years at cohort entry.
  
  
  METHODS
  None.
  
  
  METHODS
  Selected birth outcomes, including preterm birth (PTB, <37 weeks' gestation), low birth weight (<2,500 g), small for gestational age, large for gestational age, and placental disorders, ascertained from the Danish Medical Birth Registry and Danish National Registry of Patients. Risk ratios (RRs) and 95% confidence intervals (CIs) were estimated using log-binomial regression, with adjustment for potential confounders and fertility treatment.
  
  
  RESULTS
  Multivariable RRs for PTB in relation to TTP of 3-5, 6-11, and ≥12 vs. <3 cycles were 1.59 (95% CI 0.94-2.69), 0.85 (95% CI 0.48-1.50), and 1.57 (95% CI 0.93-2.65). The association was slightly stronger for spontaneous PTB (TTP ≥12 vs. <3 cycles: RR 1.69, 95% CI 0.84-3.42) than for medically indicated PTB (RR 1.39, 95% CI 0.62-3.12). Longer TTPs (≥12 cycles) were associated with increased risks of low birth weight (RR 1.80, 95% CI 0.97-3.35), cesarean delivery (RR 1.64, 95% CI 1.27-2.12), placental disorders (RR 2.21, 95% CI 1.07-4.56), ischemic placental disease (RR 1.56, 95% CI 0.99-2.44), pre-eclampsia (RR 1.45, 95% CI 0.79-2.65), and postpartum hemorrhage (RR 1.58, CI 1.14-2.19), and decreased risks of macrosomia (≥4,500 g; RR 0.63, 95% CI 0.35-1.13) and large for gestational age (RR 0.76, 95% CI 0.58-1.00). Longer TTP showed little association with small for gestational age.
  
  
  CONCLUSIONS
  In a prospective cohort study of Danish pregnancy planners, delayed conception was a marker for adverse birth outcomes, after accounting for fertility treatment.
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, Massachusetts; Slone Epidemiology Center, Boston University, Boston, Massachusetts. Electronic address: lwise@bu.edu.
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Wise
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Mikkelsen
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Henrik Toft
authors.initials: HT
authors.lastname: Sørensen
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, Massachusetts; RTI Health Solutions, Research Triangle Institute, Research Triangle Park, North Carolina.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Rothman
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, Massachusetts.
authors.forename: Kristen A
authors.initials: KA
authors.lastname: Hahn
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Anders H
authors.initials: AH
authors.lastname: Riis
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, Massachusetts.
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Hatch
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D010922:Placenta Diseases / Q000453:epidemiology; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D011256:Pregnancy Outcome / Q000453:epidemiology*; D047928:Premature Birth / Q000453:epidemiology; D061685:Time-to-Pregnancy; D055815:Young Adult
keywords: Fertility; cohort study; low birth weight; preterm birth; prospective study