title: Standardisation of crown-rump length measurement.
abstract: Correct estimation of gestational age is essential for any study of ultrasound biometry and for everyday clinical practice. However, inconsistency in pregnancy dating may occur through differences in measurement methods or errors during measurement. In the INTERGROWTH-21(st) Project, pregnancies are dated by the last menstrual period, provided that it is certain and associated with a regular menstrual cycle, and the gestational age by dates concurs with a first-trimester ultrasound crown-rump length (CRL) estimation. Hence, there was a need to standardise CRL measurement methodology across the study sites in this international, multicentre project to avoid systematic differences in dating. To achieve uniformity we undertook the following steps: the ultrasound technique was standardised by disseminating an illustrated, operating manual describing CRL plane landmarks and calliper application, and posters describing the correct acquisition technique were disseminated for quick reference. To ensure that all ultrasonographers understood the methodology, they forwarded a log-book to the INTERGROWTH-21(st) Ultrasound Coordinating Unit, containing the answers to a written test on the manual material and five images of a correctly acquired CRL. Interpretation of CRL was also standardised by ensuring that the same CRL regression formula was used across all study sites. These methods should minimise potential systematic errors in dating associated with pooling data from different health institutions, and represent a model for standardising CRL measurement in future studies.
authors.affiliation: Nuffield Department of Obstetrics & Gynaecology, Oxford Maternal & Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, UK.
authors.forename: C
authors.initials: C
authors.lastname: Ioannou
authors.forename: I
authors.initials: I
authors.lastname: Sarris
authors.forename: L
authors.initials: L
authors.lastname: Hoch
authors.forename: L J
authors.initials: LJ
authors.lastname: Salomon
authors.forename: A T
authors.initials: AT
authors.lastname: Papageorghiou
mesh_terms: D002983:Clinical Competence; D002985:Clinical Protocols; D018568:Crown-Rump Length; D005260:Female; D047109:Fetal Development; D005865:Gestational Age; D057238:Growth Charts; D006801:Humans; D008137:Longitudinal Studies / Q000379:methods / Q000592:standards; D015337:Multicenter Studies as Topic / Q000379:methods / Q000592:standards*; D011247:Pregnancy; D012107:Research Design / Q000592:standards*; D016216:Ultrasonography, Prenatal / Q000295:instrumentation / Q000379:methods / Q000592:standards*
keywords: Crown-rump length; dating; gestation; growth; pregnancy; ultrasound