title: International standards for early fetal size and pregnancy dating based on ultrasound measurement of crown-rump length in the first trimester of pregnancy.
abstract: OBJECTIVE
  There are no international standards for relating fetal crown-rump length (CRL) to gestational age (GA), and most existing charts have considerable methodological limitations. The INTERGROWTH-21(st) Project aimed to produce the first international standards for early fetal size and ultrasound dating of pregnancy based on CRL measurement.
  
  
  METHODS
  Urban areas in eight geographically diverse countries that met strict eligibility criteria were selected for the prospective, population-based recruitment, between 9 + 0 and 13 + 6 weeks' gestation, of healthy well-nourished women with singleton pregnancies at low risk of fetal growth impairment. GA was calculated on the basis of a certain last menstrual period, regular menstrual cycle and lack of hormonal medication or breastfeeding in the preceding 2 months. CRL was measured using strict protocols and quality-control measures. All women were followed up throughout pregnancy until delivery and hospital discharge. Cases of neonatal and fetal death, severe pregnancy complications and congenital abnormalities were excluded from the study.
  
  
  RESULTS
  A total of 4607 women were enrolled in the Fetal Growth Longitudinal Study, one of the three main components of the INTERGROWTH-21(st) Project, of whom 4321 had a live singleton birth in the absence of severe maternal conditions or congenital abnormalities detected by ultrasound or at birth. The CRL was measured in 56 women at < 9 + 0 weeks' gestation; these were excluded, resulting in 4265 women who contributed data to the final analysis. The mean CRL and SD increased with GA almost linearly, and their relationship to GA is given by the following two equations (in which GA is in days and CRL in mm): mean CRL = -50.6562 + (0.815118 × GA) + (0.00535302 × GA(2) ); and SD of CRL = -2.21626 + (0.0984894 × GA). GA estimation is carried out according to the two equations: GA = 40.9041 + (3.21585 × CRL(0.5) ) + (0.348956 × CRL); and SD of GA = 2.39102 + (0.0193474 × CRL).
  
  
  CONCLUSIONS
  We have produced international prescriptive standards for early fetal linear size and ultrasound dating of pregnancy in the first trimester that can be used throughout the world.
authors.affiliation: Nuffield Department of Obstetrics & Gynaecology and Oxford Maternal & Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, UK.
authors.forename: A T
authors.initials: AT
authors.lastname: Papageorghiou
authors.forename: S H
authors.initials: SH
authors.lastname: Kennedy
authors.forename: L J
authors.initials: LJ
authors.lastname: Salomon
authors.forename: E O
authors.initials: EO
authors.lastname: Ohuma
authors.forename: L
authors.initials: L
authors.lastname: Cheikh Ismail
authors.forename: F C
authors.initials: FC
authors.lastname: Barros
authors.forename: A
authors.initials: A
authors.lastname: Lambert
authors.forename: M
authors.initials: M
authors.lastname: Carvalho
authors.forename: Y A
authors.initials: YA
authors.lastname: Jaffer
authors.forename: E
authors.initials: E
authors.lastname: Bertino
authors.forename: M G
authors.initials: MG
authors.lastname: Gravett
authors.forename: D G
authors.initials: DG
authors.lastname: Altman
authors.forename: M
authors.initials: M
authors.lastname: Purwar
authors.forename: J A
authors.initials: JA
authors.lastname: Noble
authors.forename: R
authors.initials: R
authors.lastname: Pang
authors.forename: C G
authors.initials: CG
authors.lastname: Victora
authors.forename: Z A
authors.initials: ZA
authors.lastname: Bhutta
authors.forename: J
authors.initials: J
authors.lastname: Villar
mesh_terms: D000328:Adult; D018568:Crown-Rump Length; D005260:Female; D005865:Gestational Age; D057238:Growth Charts; D006801:Humans; D008137:Longitudinal Studies; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal
keywords: crown-rump length; dating; gestational age; global health; growth; pregnancy