title: Presence of the sickle cell trait and preterm delivery in African-American women.
abstract: OBJECTIVE
  To estimate the association between presence of the sickle cell trait and preterm delivery among African-American women.
  
  
  METHODS
  A retrospective cohort study was conducted to study all deliveries by African-American women at one institution between 1976 and 2001. The primary predictor of interest was the presence of the sickle cell trait, and the primary outcome was preterm delivery. Post hoc analyses were conducted to explore the relationship between presence of sickle cell trait and multiple gestations, an apparent modifier of the relationship between sickle cell trait and preterm delivery.
  
  
  RESULTS
  Of the 5,028 African-American women eligible for inclusion, 6.5% carried the sickle cell trait. In adjusted analyses, the presence of sickle cell trait was associated with a lower risk of preterm delivery at less than 32 weeks (adjusted odds ratio 0.15, 95% confidence interval 0.05-0.49), and was found to be associated with an increased odds of multiple gestations (adjusted odds ratio 1.94, 95% confidence interval 1.22-2.09). A significant interaction exists between the presence of multiple gestation and sickle cell trait and the odds of preterm delivery, such that the protective effect of sickle cell trait on preterm delivery risk is greater among those with multiple gestations than those with singletons.
  
  
  CONCLUSIONS
  Among African-American women, the presence of the sickle cell trait was associated with lower odds of early preterm delivery despite adjustment for potential confounders. An increased odds of multiple gestations was also noted among these women, possibly suggesting a persistence of selection for the hemoglobin S trait in nonmalarial settings.
  
  
  METHODS
  II.
authors.affiliation: Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco 94143-0132, USA. bryanta@obgyn.ucsf.edu
authors.forename: Allison S
authors.initials: AS
authors.lastname: Bryant
authors.forename: Yvonne W
authors.initials: YW
authors.lastname: Cheng
authors.forename: Deirdre J
authors.initials: DJ
authors.lastname: Lyell
authors.forename: Russell K
authors.initials: RK
authors.lastname: Laros
authors.forename: Aaron B
authors.initials: AB
authors.lastname: Caughey
mesh_terms: D000293:Adolescent; D000328:Adult; D001741:Black or African American / Q000235:genetics*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007752:Obstetric Labor, Premature / Q000235:genetics*; D016017:Odds Ratio; D011247:Pregnancy; D011272:Pregnancy, Multiple; D012189:Retrospective Studies; D012307:Risk Factors; D012805:Sickle Cell Trait