International estimated fetal weight standards of the INTERGROWTH-21stProject.
Estimated fetal weight (EFW) and fetal biometry are complementary measures used to screen for fetal growth disturbances. Our aim was to provide international EFW standards to complement the INTERGROWTH-21stFetal Growth Standards that are available for use worldwide.



Women with an accurate gestational-age assessment, who were enrolled in the prospective, international, multicenter, population-based Fetal Growth Longitudinal Study (FGLS) and INTERBIO-21stFetal Study (FS), two components of the INTERGROWTH-21stProject, had ultrasound scans every 5 weeks from 9-14 weeks' until 40 weeks' gestation. At each visit, measurements of fetal head circumference (HC), biparietal diameter, occipitofrontal diameter, abdominal circumference (AC) and femur length (FL) were obtained blindly by dedicated research sonographers using standardized methods and identical ultrasound machines. Birth weight was measured within 12 h of delivery by dedicated research anthropometrists using standardized methods and identical electronic scales. Live babies without any congenital abnormality, who were born within 14 days of the last ultrasound scan, were selected for inclusion. As most births occurred at around 40 weeks' gestation, we constructed a bootstrap model selection and estimation procedure based on resampling of the complete dataset under an approximately uniform distribution of birth weight, thus enriching the sample size at extremes of fetal sizes, to achieve consistent estimates across the full range of fetal weight. We constructed reference centiles using second-degree fractional polynomial models.



Of the overall population, 2404 babies were born within 14 days of the last ultrasound scan. Mean time between the last scan and birth was 7.7 (range, 0-14) days and was uniformly distributed. Birth weight was best estimated as a function of AC and HC (without FL) as log(EFW) = 5.084820 - 54.06633 × (AC/100)3- 95.80076 × (AC/100)3× log(AC/100) + 3.136370 × (HC/100), where EFW is in g and AC and HC are in cm. All other measures, gestational age, symphysis-fundus height, amniotic fluid indices and interactions between biometric measures and gestational age, were not retained in the selection process because they did not improve the prediction of EFW. Applying the formula to FGLS biometric data (n = 4231) enabled gestational age-specific EFW tables to be constructed. At term, the EFW centiles matched those of the INTERGROWTH-21stNewborn Size Standards but, at < 37 weeks' gestation, the EFW centiles were, as expected, higher than those of babies born preterm. Comparing EFW cross-sectional values with the INTERGROWTH-21stPreterm Postnatal Growth Standards confirmed that preterm postnatal growth is a different biological process from intrauterine growth.



We provide an assessment of EFW, as an adjunct to routine ultrasound biometry, from 22 to 40 weeks' gestation. However, we strongly encourage clinicians to evaluate fetal growth using separate biometric measures such as HC and AC, as well as EFW, to avoid the minimalist approach of focusing on a single value. © 2016 Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.
Maternité Necker-Enfants Malades, AP-HP & EA7328 Université Paris Descartes, Paris, France.
J
J
Stirnemann
Nuffield Department of Obstetrics & Gynaecology and Oxford Maternal & Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, UK.
J
J
Villar
Maternité Necker-Enfants Malades, AP-HP & EA7328 Université Paris Descartes, Paris, France.|Collège Français d'Echographie Foetale - CFEF, France.
L J
LJ
Salomon
Nuffield Department of Obstetrics & Gynaecology and Oxford Maternal & Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, UK.|Centre for Statistics in Medicine, Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, University of Oxford, Oxford, UK.
E
E
Ohuma
School of Public Health, Peking University, Beijing, China.
P
P
Ruyan
Centre for Statistics in Medicine, Nuffield Department of Orthopaedics, Rheumatology & Musculoskeletal Sciences, University of Oxford, Oxford, UK.
D G
DG
Altman
Shoklo Malaria Research Unit, Maesod, Tak, Thailand.
F
F
Nosten
Nuffield Department of Obstetrics & Gynaecology and Oxford Maternal & Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, UK.
R
R
Craik
Division of Women & Child Health, The Aga Khan University, Karachi, Pakistan.
S
S
Munim
Nuffield Department of Obstetrics & Gynaecology and Oxford Maternal & Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, UK.
L
L
Cheikh Ismail
Programa de Pós-Graduação em Saúde e Comportamento, Universidade Católica de Pelotas, Pelotas, RS, Brazil.|Programa de Pós-Graduação em Epidemiologia, Universidade Federal de Pelotas, Pelotas, RS, Brazil.
F C
FC
Barros
Nuffield Department of Obstetrics & Gynaecology and Oxford Maternal & Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, UK.
A
A
Lambert
Developmental Pathways For Health Research Unit, Department of Paediatrics & Child Health, University of the Witwatersrand, Johannesburg, South Africa.
S
S
Norris
Faculty of Health Sciences, Aga Khan University, Nairobi, Kenya.
M
M
Carvalho
Department of Family & Community Health, Ministry of Health, Muscat, Sultanate of Oman.
Y A
YA
Jaffer
Department of Engineering Science, University of Oxford, Oxford, UK.
J A
JA
Noble
Dipartimento di Scienze Pediatriche e dell'Adolescenza, Cattedra di Neonatologia, Università degli Studi di Torino, Torino, Italy.
E
E
Bertino
Global Alliance to Prevent Prematurity and Stillbirth (GAPPS), Seattle, WA, USA.
M G
MG
Gravett
Nagpur INTERGROWTH-21st Research Centre, Ketkar Hospital, Nagpur, India.
M
M
Purwar
Programa de Pós-Graduação em Epidemiologia, Universidade Federal de Pelotas, Pelotas, RS, Brazil.
C G
CG
Victora
Division of Paediatrics, Pontifical Universidad Catolica de Chile, Chile.|London School of Hygiene and Tropical Medicine, London, UK.
R
R
Uauy
Center for Global Child Health, Hospital for Sick Children, Toronto, ON, Canada.
Z
Z
Bhutta
Nuffield Department of Obstetrics & Gynaecology and Oxford Maternal & Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, UK.
S
S
Kennedy
Nuffield Department of Obstetrics & Gynaecology and Oxford Maternal & Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, UK.
A T
AT
Papageorghiou
D000328:Adult; D001724:Birth Weight; D003430:Cross-Sectional Studies; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000196:embryology; D020567:Fetal Weight; D005865:Gestational Age; D006257:Head / Q000000981:diagnostic imaging* / Q000196:embryology; D006801:Humans; D011247:Pregnancy; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal / Q000379:methods*
birth weight; fetal growth; gestational age; screening; ultrasound