title: Maternal 25-hydroxyvitamin d and preterm birth in twin gestations.
abstract: OBJECTIVE
  To assess whether there was an independent association between maternal 25-hydroxyvitamin D concentrations at 24-28 weeks of gestation and preterm birth in a multicenter U.S. cohort of twin pregnancies.
  
  
  METHODS
  Serum samples from women who participated in a clinical trial of 17 α-hydroxyprogesterone caproate for the prevention of preterm birth in twin gestations (2004-2006) were assayed for 25-hydroxyvitamin D concentrations using liquid chromatography tandem mass spectrometry (n=211). Gestational age was determined early in pregnancy using a rigorous algorithm. Preterm birth was defined as delivery of the first twin or death of either twin at less than 35 weeks of gestation.
  
  
  RESULTS
  The mean serum 25-hydroxyvitamin D concentration was 82.7 nmol/L (standard deviation 31.5); 40.3% of women had concentrations less than 75 nmol/L. Preterm birth at less than 35 weeks of gestation occurred in 49.4% of women with 25-hydroxyvitamin D concentrations less than 75 nmol/L compared with 26.2% among those with concentrations of 75 nmol/L or more (P<.001). After adjustment for maternal race and ethnicity, study site, parity, prepregnancy body mass index, season, marital status, education, gestational age at blood sampling, smoking status, and 17 α-hydroxyprogesterone caproate treatment, maternal 25-hydroxyvitamin D concentration of 75 nmol/L or more was associated with a 60% reduction in the odds of preterm birth compared with concentrations less than 75 nmol/L (adjusted odds ratio [OR] 0.4, 95% confidence interval [CI] 0.2-0.8). A similar protective association was observed when studying preterm birth at less than 32 weeks of gestation (OR 0.2, 95% CI 0.1-0.6) and after confounder adjustment.
  
  
  CONCLUSIONS
  Late second-trimester maternal 25-hydroxyvitamin D concentrations less than 75 nmol/L are associated with an increase in the risk of preterm birth in this cohort of twin pregnancies.
  
  
  METHODS
  II.
authors.affiliation: Departments of Epidemiology and Obstetrics and Gynecology, University of Pittsburgh Pittsburgh, Pennsylvania, University of Alabama at Birmingham, Birmingham, Alabama, Northwestern University, Chicago, Illinois, Drexel University, Philadelphia, Pennsylvania, University of Utah, Salt Lake City, Utah, Columbia University, New York, New York, The Ohio State University, Columbus, Ohio, Case Western Reserve University-MetroHealth Medical Center, Cleveland, Ohio, University of North Carolina, Chapel Hill, North Carolina, Wayne State University, Detroit, Michigan, Brown University, Providence, Rhode Island, University of Texas Southwestern Medical Center, Dallas, Texas, University of Texas Health Science Center at Houston, Houston, Texas, and Wake Forest University Health Sciences, Winston-Salem, North Carolina; the George Washington University Biostatistics Center, Washington, DC; and the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Bodnar
authors.forename: Dwight J
authors.initials: DJ
authors.lastname: Rouse
authors.forename: Valerija
authors.initials: V
authors.lastname: Momirova
authors.forename: Alan M
authors.initials: AM
authors.lastname: Peaceman
authors.forename: Anthony
authors.initials: A
authors.lastname: Sciscione
authors.forename: Catherine Y
authors.initials: CY
authors.lastname: Spong
authors.forename: Michael W
authors.initials: MW
authors.lastname: Varner
authors.forename: Fergal D
authors.initials: FD
authors.lastname: Malone
authors.forename: Jay D
authors.initials: JD
authors.lastname: Iams
authors.forename: Brian M
authors.initials: BM
authors.lastname: Mercer
authors.forename: John M
authors.initials: JM
authors.lastname: Thorp
authors.forename: Yoram
authors.initials: Y
authors.lastname: Sorokin
authors.forename: Marshall W
authors.initials: MW
authors.lastname: Carpenter
authors.forename: Julie
authors.initials: J
authors.lastname: Lo
authors.forename: Susan M
authors.initials: SM
authors.lastname: Ramin
authors.forename: Margaret
authors.initials: M
authors.lastname: Harper
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D059285:Pregnancy, Twin / Q000097:blood*; D047928:Premature Birth / Q000097:blood* / Q000453:epidemiology; D018570:Risk Assessment; D012307:Risk Factors; D014481:United States; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood*; D055815:Young Adult
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D