title: Interpregnancy interval after live birth or pregnancy termination and estimated risk of preterm birth: a retrospective cohort study.
abstract: We assessed whether interpregnancy interval (IPI) length after live birth and after pregnancy termination was associated with preterm birth (PTB).
  
  
  
  Multiyear birth cohort.
  
  
  
  Fetal death, birth and infant death certificates in California merged with Office of Statewide Health Planning and Development.
  
  
  
  One million California live births (2007-10) after live birth and after pregnancy termination.
  
  
  
  Logistic regression was used to estimate odds ratios (ORs) of PTB of 20-36 weeks of gestation and its subcategories for IPIs after a live birth and after a pregnancy termination. We used conditional logistic regression (two IPIs/mother) to investigate associations within mothers.
  
  
  
  PTB relative to gestations of ≥ 37 weeks.
  
  
  
  Analyses included 971 211 women with IPI after live birth, and 138 405 women with IPI after pregnancy termination with 30.6% and 74.6% having intervals of <18 months, respectively. IPIs of <6 months or 6-11 months after live birth showed increased odds of PTB adjusted ORs for PTB of 1.71 (95% CI 1.65-1.78) and 1.20 (95% CI 1.16-1.24), respectively compared with intervals of 18-23 months. An IPI >36 months (versus 18-23 months) was associated with increased odds for PTB. Short IPI after pregnancy termination showed a decreased OR of 0.87 (95% CI 0.81-0.94). The within-mother analysis showed the association of increased odds of PTB for short IPI, but not for long IPI.
  
  
  
  Women with IPI <1 or >3 years after a live birth were at increased odds of PTB-an important group for intervention to reduce PTB. Short IPI after pregnancy termination was associated with reduced odds for PTB and needs to be further explored.
  
  
  
  Short and long IPI after live birth, but not after pregnancy termination, showed increased odds for PTB.
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA. bettyshachar@gmail.com, bshachar@stanford.edu.
authors.forename: B Z
authors.initials: BZ
authors.lastname: Shachar
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Mayo
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Lyell
authors.affiliation: Department of Pediatrics, University of California San Diego, La Jolla, CA, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Baer
authors.affiliation: Department of Epidemiology and Biostatistics, University of California, San Francisco, School of Medicine, San Francisco, CA, USA.
authors.forename: L L
authors.initials: LL
authors.lastname: Jeliffe-Pawlowski
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Stevenson
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: G M
authors.initials: GM
authors.lastname: Shaw
mesh_terms: D000028:Abortion, Induced / Q000009:adverse effects*; D000328:Adult; D001721:Birth Intervals / Q000706:statistics & numerical data*; D015992:Body Mass Index; D002140:California / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D005313:Fetal Death / Q000209:etiology*; D005865:Gestational Age; D006801:Humans; D015994:Incidence; D007223:Infant; D007226:Infant Mortality; D007231:Infant, Newborn; D050498:Live Birth / Q000453:epidemiology; D008423:Maternal Age; D009765:Obesity / Q000453:epidemiology; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology* / Q000209:etiology*; D012189:Retrospective Studies; D012307:Risk Factors
keywords: Interpregnancy interval; preterm birth; prevention; risk assessment