title: Determinants and consequences of discrepancies in menstrual and ultrasonographic gestational age estimates.
abstract: OBJECTIVE
  To assess the association between maternal and fetal characteristics and discrepancy between last normal menstrual period and early (<20 weeks) ultrasound-based gestational age and the association between discrepancies and pregnancy outcomes.
  
  
  METHODS
  Hospital-based cohort study.
  
  
  METHODS
  Montreal, Canada.
  
  
  METHODS
  A total of 46,514 women with both menstrual- and early ultrasound-based gestational age estimates.
  
  
  METHODS
  Positive (last normal menstrual period > early ultrasound, i.e. menstrual-based gestational age is higher than early ultrasound-based gestational age, so that the expected date of delivery is earlier with the menstrual-based gestational age) discrepancies > or =+7 days, mean birthweight, low birthweight, stillbirth and in-hospital neonatal death.
  
  
  RESULTS
  Multiparous mothers and those with diabetes, small stature or high pre-pregnancy body mass index were more likely to have positive discrepancies. The proportion of women with discrepancies > or =+7 days was significantly higher among chromosomally malformed and female fetuses. The mean birthweight declined with increasingly positive differences. The risk of low birthweight was significantly higher for positive differences. Associations with fetal growth measures were more plausible with early ultrasound estimates.
  
  
  CONCLUSIONS
  Although most discrepancies between last normal menstrual period- and early ultrasound-based gestational age are attributable to errors in menstrual dating, our results suggest that some positive differences reflect early growth restriction.
authors.affiliation: Department of Pediatrics, McGill University Faculty of Medicine, Montreal, Quebec, Canada.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Morin
authors.forename: Lucie
authors.initials: L
authors.lastname: Morin
authors.forename: Xun
authors.initials: X
authors.lastname: Zhang
authors.forename: Robert W
authors.initials: RW
authors.lastname: Platt
authors.forename: Béatrice
authors.initials: B
authors.lastname: Blondel
authors.forename: Gérard
authors.initials: G
authors.lastname: Bréart
authors.forename: Robert
authors.initials: R
authors.lastname: Usher
authors.forename: Michael S
authors.initials: MS
authors.lastname: Kramer
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007230:Infant, Low Birth Weight / Q000502:physiology; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age / Q000502:physiology; D008598:Menstruation; D015999:Multivariate Analysis; D011247:Pregnancy; D012307:Risk Factors; D013997:Time Factors; D016216:Ultrasonography, Prenatal / Q000592:standards*