title: Ethnic heterogeneity in the longitudinal effects of placental vascular blood flow on birthweight.
abstract: OBJECTIVE
  Our goals were: (1) to estimate the longitudinal trends in uterine artery (UtArt) and umbilical artery (UmArt) resistance indices (RIs) in different ethnic strata; (2) to estimate time-dependent changes across gestation in the influence of variation in UtArt and UmArt RI on variation in birthweight in different ethnic strata; and (3) to determine the optimum set of UtArt and UmArt RIs for predicting birthweight in different ethnic strata.
  
  
  METHODS
  Analyses were carried out on data collected in a prospective study of 535 multiethnic gravidas recruited from the Cedars-Sinai Medical Center (Los Angeles, CA). Baseline maternal characteristics were recorded at time of entry into the study. UtArt and UmArt RIs were measured on 3 occasions during pregnancy (visit 1, 16-20 weeks' gestation; visit 2, 21-29 weeks' gestation; and visit 3, 30-36 weeks' gestation). The outcome for this study was gestational age-adjusted birthweight (aBW).
  
  
  RESULTS
  The average UtArt and UmArt RI decreased steadily across gestation for all ethnicities. The average UtArt RI at each visit and the average rate of change between visits were not significantly different among the ethnicities. However, the UmArt RI measured at visit 3 and its rate of change in the last trimester were significantly different among the ethnic groups (P < .02). After adjustment for traditional risk factors for fetal growth restriction, the magnitude and rate of change of UtArt RI significantly predicted aBW only in Hispanic women, whereas the magnitude and rate of change of UmArt RI predicted aBW only in African American women. The most parsimonious combination of UtArt and UmArt RI measurements at visits 1, 2, and 3 that predicted statistically significant variation in aBW differed by ethnicity.
  
  
  CONCLUSIONS
  The relationships between aBW and longitudinally collected measures of UtArt and UmArt RI depend on the context defined by ethnicity and time of measurement after adjusting for a parsimoniously selected subset of traditional risk factors.
authors.affiliation: Division of Medical Genetics, Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Vinod K
authors.initials: VK
authors.lastname: Misra
authors.forename: Calvin J
authors.initials: CJ
authors.lastname: Hobel
authors.forename: Charles F
authors.initials: CF
authors.lastname: Sing
mesh_terms: D000293:Adolescent; D000328:Adult; D001741:Black or African American / Q000706:statistics & numerical data; D001724:Birth Weight / Q000502:physiology*; D001783:Blood Flow Velocity; D016001:Confidence Intervals; D005006:Ethnicity / Q000706:statistics & numerical data*; D005260:Female; D005865:Gestational Age; D006630:Hispanic or Latino / Q000706:statistics & numerical data; D006801:Humans; D008137:Longitudinal Studies; D008423:Maternal Age; D021041:Placental Circulation / Q000502:physiology*; D011237:Predictive Value of Tests; D011247:Pregnancy; D011256:Pregnancy Outcome; D011295:Prenatal Care; D011336:Probability; D011446:Prospective Studies; D014469:Umbilical Arteries / Q000502:physiology; D014599:Uterus / Q000098:blood supply; D014655:Vascular Resistance; D044465:White People / Q000706:statistics & numerical data