Customized assessment resulted in increased identification of small for gestational age and stillbirth risk, while the wide variation in SGA rates using the INTERGROWTH-21 standard appeared to mostly reflect differences in physiological pregnancy characteristics in the 10 maternity populations.

What are the novel findings of this work?We have defined limits for normal, slow and accelerated fetal growth which are specific to the ultrasound measurement interval, have a false-positive rate limited to 10% and are associated with perinatal outcome. Two-thirds of pregnancies at increased risk of stillbirth due to slow growth were not small-for-gestational age at the last scan. What are the clinical implications of this work?This method for defining normal and abnormal fetal growth presents an additional, size-independent parameter for antenatal surveillance by serial fetal biometry. Greater emphasis on monitoring growth velocity will help identify pregnancies at risk and prevent adverse perinatal outcome.

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What are the novel findings of this work? There has been a sustained decline in stillbirths in England, which coincided with increased awareness of fetal growth restriction as a potentially avoidable cause of stillbirth, and guidelines to improve antenatal detection. The reduction in stillbirth rates has been accelerated through implementation of the Growth Assessment Protocol. What are the clinical implications of this work? The study found a dose dependent relationship between adherence to evidence based risk assessment and growth surveillance, and extent of benefit gained; units with best antenatal detection rates of SGA had the steepest decline in stillbirth rates, which emphasises the need to prioritise this aspect of maternity service provision. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as

OBJECTIVE: Fetal growth restriction is associated with stillbirth and other adverse pregnancy outcomes, and use of the correct weight standard is an essential proxy indicator of growth status and perinatal risk. We sought to assess the performance of two international birthweight standards for their ability to identify perinatal morbidity and mortality indicators associated with small for gestational age (SGA) infants. STUDY DESIGN: This retrospective cohort study used data from a multi-center quality initiative including a multi-ethnic dataset of 125826 births from 2012e2017. Of the singleton term births available, 96142 had complete outcome data including stillbirth, neonatal death, 5-minute Apgar, glucose instability and need for newborn transfer to a higher level of care or NICU admission. The customized (GROW) and INTERGROWTH-21 st (IG21) birthweight standards were applied to determine SGA according to their respective methods and formulae. Associations with adverse outcomes were expressed as odds ratios (OR) with 95% confidence intervals (CI) and population attributable risk (PAR). RESULTS: GROW classified 10479 (10.9%) and IG21 classified 4282 (4.5%) pregnancies as SGA, respectively. For all of the outcomes assessed, GROW identified more SGA infants with adverse outcomes than IG21 did, including more with stillbirth, perinatal death, low Apgar (<7), glucose instability and transfers to a higher level of care (Table 1). In the case of stillbirth, 14 of the 29 cases (48%) that were SGA by either method were identified as SGA by GROW only and not by IG21. Similarly, additional cases of all other adverse outcome indicators were identified by GROW as SGA, while only in one category (glucose instability) did IG21 identify 7 of 315 cases (2.2%) which were not identified as SGA by GROW. CONCLUSION: Customized assessment using GROW results in increased identification of small for gestational age babies that are at significantly increased risk of an array of adverse pregnancy outcomes.