title: Effects of race/ethnicity and BMI on the association between height and risk for spontaneous preterm birth.
abstract: OBJECTIVE
  Short height and obesity have each been associated with increased risk for preterm birth (PTB). However, the effect of short height on PTB risk, across different race/ethnicities and body mass index (BMI) categories, has not been studied. Our objective was to determine the influence of maternal height on the risk for PTB within race/ethnic groups, BMI groups, or adjusted for weight.
  
  
  METHODS
  All California singleton live births from 2007 through 2010 were included from birth certificate data (vital statistics) linked to hospital discharge data. Prepregnancy BMI (kg/m(2)) was categorized as underweight (<18.5), normal (18.5-24.9), overweight (25.0-29.9), or obese (≥30.0). Maternal race/ethnicity was categorized as: non-Hispanic white, non-Hispanic black, Hispanic, and Asian. Maternal height was classified into 5 categories (shortest, short, middle, tall, tallest) based on racial/ethnic-specific height distributions, with the middle category serving as reference. Poisson regression models were used to estimate relative risks for the association between maternal height and risk of spontaneous PTB (<37 weeks and <32 weeks). Models were stratified on race/ethnicity and BMI. Generalized additive regression models were used to detect nonlinearity of the association. Covariates considered were: maternal age, weight, parity, prenatal care, education, medical payment, previous PTB, gestational and pregestational diabetes, pregestational hypertension, preeclampsia/eclampsia, and smoking.
  
  
  RESULTS
  Among 1,655,385 California singleton live births, 5.2% were spontaneous PTB <37 weeks. Short stature (first height category) was associated with increased risk for PTB for non-Hispanic whites and Hispanics across all BMI categories. Among obese women, tall stature (fifth category) was associated with reduced risk for spontaneous PTB for non-Hispanic whites, Asians, and Hispanics. The same pattern of association was seen for height and risk for spontaneous PTB <32 weeks. In the generalized additive regression model plots, short stature was associated with increased risk for spontaneous PTB of <32 and <37 weeks of gestation among whites and Asians. However, this association was not observed for blacks and Hispanics.
  
  
  CONCLUSIONS
  Maternal shorter height is associated with a modest increased risk for spontaneous PTB regardless of BMI. Our results suggest that PTB risk assessment should consider race/ethnicity-specific height with respect to the norm in addition to BMI assessment.
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA. Electronic address: bshachar@stanford.edu.
authors.forename: Bat Zion
authors.initials: BZ
authors.lastname: Shachar
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Mayo
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA; California Perinatal Quality Care Collaborative, Stanford, CA.
authors.forename: Henry C
authors.initials: HC
authors.lastname: Lee
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA.
authors.forename: Suzan L
authors.initials: SL
authors.lastname: Carmichael
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA.
authors.forename: David 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.
authors.forename: Gary M
authors.initials: GM
authors.lastname: Shaw
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA; California Perinatal Quality Care Collaborative, Stanford, CA.
authors.forename: Jeffery B
authors.initials: JB
authors.lastname: Gould
mesh_terms: D000328:Adult; D001827:Body Height / Q000502:physiology; D015992:Body Mass Index; D002140:California / Q000453:epidemiology; D005260:Female; D006801:Humans; D009035:Mothers; D047928:Premature Birth / Q000453:epidemiology* / Q000208:ethnology / Q000503:physiopathology; D012307:Risk Factors; D055815:Young Adult
keywords: body mass index; maternal height; race/ethnicity; spontaneous preterm birth