Abstract Objective To investigate the screen positive rates of standards for fetal weight assessment in current use in England. Design Population based cohort study of electronic data recorded as part of routine antenatal care. Setting Integrated care boards of the National Health Service (NHS) in England. Participants 3 201 199 women with singleton pregnancies delivered between 2015 and 2025. Main outcome measures Rates of small for gestational age (birth weight 90th and >97th centile) according to seven fetal weight standards. Six of these standards are unadjustable for maternal characteristics: Hadlock (United States, single centre data), INTERGROWTH-21st (IG21, versions 2017 and 2020; eight country average), World Health Organization (WHO, 10 country average); Fetal Medicine Foundation (FMF, two NHS units average); GROW Lite (NHS population average); and GROW (NHS population, customised for each pregnancy according to maternal height, weight, parity, and ethnic origin). Results Data were available for 38 (90%) of the 42 integrated care boards in England. Overall, maternal characteristics varied widely among integrated care boards, including ethnic origin (average proportion English: 65.6%, range 19.8-92.2) and high body mass index (≥30: mean 24.8%, range 16.3-29.4). The overall rate of babies identified as being small for gestational age (90th centile) rates ranged from 4.9% for Hadlock to 17.7% for IG21-2017. Similarly, large variations were seen with cut-off points of 97th centile. Across all integrated care boards, the range of small for gestational age was wider with unadjustable standards and mostly reflected local population characteristics, including ethnicity and maternal weight. The customised GROW standard had small and large for gestational age rates of 13.4% and 8.4%, respectively, and the narrowest range of small for gestational age rates across integrated care boards (11.6-15.2%). For births at term (≥37+0 weeks), average small for gestational age rates were lowest for IG21-2017 (4.8%), highest for WHO and FMF (both 17.2%), and 12.3% for GROW. Conclusion One-size-fits-all fetal growth charts do not reflect birthweight average, distribution, and variation in our maternity population, and systematically fail to identify fetuses that are small or large for gestational age. These fetuses are potentially at risk because of restricted or accelerated growth. The heterogeneity in the NHS requires a customised standard based on the growth potential of each baby. Evidence based national guidelines are needed to standardise charts used for fetal growth assessment, for personalised and safe clinical care, and to enable proper audit and benchmarking of performance.
Gardosi et al. (Wed,) studied this question.
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