title: Ultrasound prediction of perinatal outcome: the unrecognised value of sibling data.
abstract: OBJECTIVE
  To identify high-risk fetuses at the first routinely performed ultrasound examination by making use of information from the mother's previous pregnancy.
  
  
  METHODS
  A population-based cohort study.
  
  
  METHODS
  Norway, 1999-2009.
  
  
  METHODS
  All singleton first live births and their second-born siblings registered in the Medical Birth Registry of Norway (166,786 eligible sibling pairs).
  
  
  METHODS
  Odds ratios were calculated by logistic regression.
  
  
  METHODS
  Very small for gestational age (vSGA; birthweight ≤-1.96 standard deviations) and perinatal death (stillbirth at ≥22 weeks of gestation or death within 28 days of life).
  
  
  RESULTS
  Small fetal size at ultrasound (i.e. a fetus smaller than expected by last menstrual period, LMP) is only weakly predictive of vSGA or perinatal death; however, if the firstborn sibling was vSGA at birth, ultrasound measures in the next pregnancy become strongly informative of risk. The smaller the fetal size on ultrasound, the higher its risk of vSGA (3-18%; Ptrend < 0.0001) and perinatal death (4-19 per thousand, Ptrend = 0.012). In contrast, if the first baby was not vSGA, small fetal size on ultrasound is uninformative.
  
  
  CONCLUSIONS
  When the firstborn baby is vSGA, discrepancies between fetal size on ultrasound and LMP become highly predictive of risk of vSGA and perinatal mortality in the second-born infant. The value of combining these routinely collected clinical data has not previously been recognised.
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.|Department of Clinical Sciences, University of Bergen, Bergen, Norway.
authors.forename: N-H
authors.initials: NH
authors.lastname: Morken
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.|Norwegian Institute of Public Health, Bergen, Norway.
authors.forename: R
authors.initials: R
authors.lastname: Skjaerven
authors.affiliation: Epidemiology Branch, NIEHS/NIH, Durham, NC, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Wilcox
mesh_terms: D000328:Adult; D001722:Birth Order; D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D009664:Norway / Q000453:epidemiology; D016017:Odds Ratio; D054238:Perinatal Mortality; D011237:Predictive Value of Tests; D011247:Pregnancy; D035781:Siblings; D050497:Stillbirth; D016216:Ultrasonography, Prenatal / Q000706:statistics & numerical data
keywords: Fetal size; perinatal mortality; prediction; small for gestational age; ultrasound