International estimated fetal weight standards of the INTERGROWTH‐21^st Project

Abstract

ObjectiveEstimated 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‐21st Fetal Growth Standards that are available for use worldwide.MethodsWomen with an accurate gestational‐age assessment, who were enrolled in the prospective, international, multicenter, population‐based Fetal Growth Longitudinal Study (FGLS) and INTERBIO‐21st Fetal Study (FS), two components of the INTERGROWTH‐21st Project, 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.ResultsOf 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‐21st Newborn 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‐21st Preterm Postnatal Growth Standards confirmed that preterm postnatal growth is a different biological process from intrauterine growth.ConclusionsWe 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...

Fetal growth standards: the NICHD fetal growth study approach in context with INTERGROWTH-21st and the World Health Organization Multicentre Growth Reference Study

“…It is important to note that NICHD and WHO Fetal calculated EFW from HC, AC and FL using the Hadlock 1985 formula, 26 while INTERGROWTH created a new formula 12 based on only HC and AC: INTERGROWTH: created a new formula (based on HC and AC) 12 Log(EFW) = 5.084820 − 54.06633×(AC/100) 3 − 95.80076×(AC/100) 3 ×log(AC/100) + 3.136370 ×(HC/100) NICHD and WHO Fetal: Hadlock 1985 (based on HC, AC and FL) 26 Log 10 weight = 1.326 − 0.00326 AC × FL + 0.0107 HC + 0.0438 AC + 0.158 FL…”

“…In light of critical data gaps about optimal fetal growth to aid clinical management of pregnant women, three longitudinal cohort studies were undertaken and provide new insights about contemporary fetal growth and how best to assess fetal growth: one in the U.S., the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Fetal Growth Studies 9, 10 and two international, INTERGROWTH-21 st (INTERGROWTH) 11, 12 and World Health Organization Multicentre Growth Reference Study (WHO Fetal). 13, 14 However, each has slightly different research aims that impact interpretation of findings.…”

Research standardization tools: pregnancy measures in the PhenX Toolkit

“…23 The protocol is accessible and easy to use, and it does not require major equipment or specialized training. A second protocol, the International Fetal and Newborn Consortium for the 21st Century (INTERGROWTH-21st) fetal growth standards was also considered, 24 partly because the standards were developed utilizing methods of the World Health Organization Multicenter Growth Reference Study to complete the Fetal Growth and Longitudinal Study. The PWG recommended these standards as Supplemental Information because debate still exists as to whether pooling of data across the eight geographically diverse study sites was the optimal approach and also because the EFW used to calculate the fetal growth percentiles has not yet been tested outside of the original study.…”

Disadvantages of a weight estimation formula for macrosomic fetuses: the Hart formula from a clinical perspective

“…Large numbers of fetal weight estimation formulas have been published in recent decades—but new formulas are still being added every year [20]. Virtually every measurable fetal or maternal factor has been incorporated into such formulas.…”