title: Fetal size monitoring and birth-weight prediction: a new population-based approach.
abstract: OBJECTIVE
  To develop a complete, population-based system for ultrasound-based fetal size monitoring and birth-weight prediction for use in the second and third trimesters of pregnancy.
  
  
  METHODS
  Using 31 516 ultrasound examinations from a population-based Norwegian clinical database, we constructed fetal size charts for biparietal diameter, femur length and abdominal circumference from 24 to 42 weeks' gestation. A reference curve of median birth weight for gestational age was estimated using 45 037 birth weights. We determined how individual deviations from the expected ultrasound measures predicted individual percentage deviations from expected birth weight. The predictive quality was assessed by explained variance of birth weight and receiver-operating characteristics curves for prediction of small-for-gestational age. A curve for intrauterine estimated fetal weight was constructed. Charts were smoothed using the gamlss non-linear regression method.
  
  
  RESULTS
  The population-based approach, using bias-free ultrasound gestational age, produces stable estimates of size-for-age and weight-for-age curves in the range 24-42 weeks' gestation. There is a close correspondence between percentage deviations and percentiles of birth weight by gestational age, making it easy to convert between the two. The variance of birth weight that can be 'explained' by ultrasound increases from 8% at 20 weeks up to 67% around term. Intrauterine estimated fetal weight is 0-106 g higher than median birth weight in the preterm period.
  
  
  CONCLUSIONS
  The new population-based birth-weight prediction model provides a simple summary measure, the 'percentage birth-weight deviation', to be used for fetal size monitoring throughout the third trimester. Predictive quality of the model can be measured directly from the population data. The model computes both median observed birth weight and intrauterine estimated fetal weight. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.
authors.affiliation: Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.|Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.
authors.forename: H K
authors.initials: HK
authors.lastname: Gjessing
authors.affiliation: Section of Medical Informatics, University of Oslo, Oslo, Norway.
authors.forename: P
authors.initials: P
authors.lastname: Grøttum
authors.affiliation: Department of Obstetrics and Gynecology, Stavanger University Hospital, Stavanger, Norway.
authors.forename: I
authors.initials: I
authors.lastname: Økland
authors.affiliation: National Center for Fetal Medicine, Department of Obstetrics and Gynecology, St Olav's University Hospital, Trondheim, Norway.|Department of Laboratory Medicine, Children's and Women's Health, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: S H
authors.initials: SH
authors.lastname: Eik-Nes
mesh_terms: D000005:Abdomen / Q000196:embryology*; D001724:Birth Weight; D049628:Body Size; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000196:embryology*; D005865:Gestational Age; D057238:Growth Charts; D006801:Humans; D007236:Infant, Small for Gestational Age; D008962:Models, Theoretical; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D016216:Ultrasonography, Prenatal / Q000379:methods*
keywords: birth weight; estimated fetal weight; fetal growth; fetal size reference curves; gestation-adjusted prediction; gestational age; population-based; ultrasound