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Objective: Fetal growth surveillance includes assessment of size as well as rate of growth, and various definitions for slow growth have been adopted into clinical use. The aim of this study was to evaluate the effectiveness of different models to identify stillbirth risk, in addition to risk represented by the fetus being small-for-gestational age (SGA)., Methods: This was a retrospective analysis of a routinely collected and anonymized dataset of pregnancies that had two or more third-trimester ultrasound measurements of estimated fetal weight (EFW). SGA was defined as EFW < 10 th customized centile, and slow growth was defined according to five published models in clinical use: (1) a fixed velocity limit of 20 g per day (FVL 20 ); (2) a fixed > 50 centile drop, regardless of scan-measurement interval (FCD 50 ); (3) a fixed > 30 centile drop, regardless of scan interval (FCD 30 ); (4) growth trajectory slower than the third customized growth-centile limit (GCL 3 ); and (5) EFW at second scan below the projected optimal weight range (POWR), based on partial receiver-operating-characteristics-curve-derived  cut-offs specific to the scan interval., Results: The study cohort consisted of 164 718 pregnancies with 480 592 third-trimester ultrasound scans (mean ± SD, 2.9 ± 0.9). The last two scans in each pregnancy were performed at an average gestational age of 33 + 5 and 37 + 1 weeks. At the last scan, 12 858 (7.8%) EFWs were SGA, and of these, 9359 were also SGA at birth (positive predictive value, 72.8%). The rate at which slow growth was defined varied considerably (FVL 20 , 12.7%; FCD 50 , 0.7%; FCD 30 , 4.6%; GCL 3 , 19.8%; POWR, 10.1%), and there was varying overlap between cases identified as having slow growth and those identified as SGA at the last scan. Only the POWR method identified additional non-SGA pregnancies with slow growth (11 237/16 671 (67.4%)) that had significant stillbirth risk (relative risk, 1.58 (95% CI, 1.04-2.39)). These non-SGA cases resulting in stillbirth had a median EFW centile of 52.6 at the last scan and a median weight centile of 27.3 at birth. Subgroup analysis identified methodological problems with the fixed-velocity model because it assumes linear growth throughout gestation, and with the centile-based methods because the non-parametric distribution of centiles at the extremes does not reflect actual difference in weight gain., Conclusion: Comparative analysis of five clinically used methods to define slow fetal growth has shown that only the measurement-interval-specific POWR model can identify non-SGA fetuses with slow growth that are at increased risk of stillbirth. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology., (© 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.)

Objective: Fetal growth assessment is central to good antenatal care, yet there is a lack of definition of normal and abnormal fetal growth rate which can identify pregnancies at risk of adverse outcome. The aim of this study was to develop and test a model for defining normal limits of growth velocity which are specific to the fetal weight measurement interval., Methods: The cohort consisted of 102 138 singleton pregnancies which underwent at least two third-trimester measurements of ultrasound estimated fetal weight (EFW), usually carried out because routine early-pregnancy risk assessment had indicated an increased risk of fetal growth restriction. We projected the EFW from the first of each consecutive measurement pair along its own centile rank to the gestational age of the second scan. Normal growth was defined as the second EFW being within a weight range based on limits derived by partial receiver-operating-characteristics-curve (pROC) analyses for small-for-gestational-age (SGA; < 10 th  centile) and large-for-gestational-age (LGA; > 90 th  centile) birth weight. The limits were measurement-interval specific and calculated for a fixed false-positive rate (FPR) of 10%. The resultant normal, slow and accelerated growth rates calculated from consecutive EFW pairs were evaluated against the following predefined perinatal outcome measures: stillbirth, neonatal death, SGA and LGA at birth, 5-min Apgar score < 7 and admission to the neonatal intensive care unit. Slow growth based on the last two scans was compared with SGA fetal weight (EFW < 10 th  centile) at the last scan and association with stillbirth risk was assessed, expressed as relative risk (RR) with 95% CI., Results: The optimal cut-off limits for normal growth rate between consecutive scans varied according to the length of the measurement interval, with an average of -8.0% for slow growth and + 9.3% for accelerated growth at a fixed FPR of 10%. Slow growth between random consecutive scan pairs was associated significantly with all predefined outcome measures including stillbirth (RR, 2.19; 95% CI, 1.84-2.53) and neonatal death (RR, 2.28; 95% CI, 1.60-3.13). Accelerated growth was associated with LGA at birth (RR, 2.15; 95% CI, 2.10-2.20), while normal growth was protective of all adverse outcome measures. Slow growth between the last two scans (which were performed at a median gestational age of 33 + 1 to 36 + 4 weeks) and SGA at the last scan were each predictors of stillbirth, and stillbirth risk was highest when both were present (RR, 2.65; 95% CI, 1.67-4.20). However, 66.2% of pregnancies with slow growth were not SGA at the last scan and these cases also had an increased risk of stillbirth (RR, 2.07; 95% CI, 1.40-3.05)., Conclusion: Fetal growth velocity defined by projected, measurement-interval specific fetal weight limits is associated independently with perinatal outcome and should be used for antenatal surveillance in addition to assessment by fetal size. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology., (© 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.)

Objective: Antenatal detection of small-for-gestational age (SGA) can reduce significantly the risk of stillbirth. The Growth Assessment Protocol (GAP) was developed to address the problem that most SGA fetuses are missed antenatally. We set out to analyze the effect that the GAP program has had on stillbirth rates in England., Methods: We analyzed data from 2008 (the year before roll-out of the GAP program) to 2017 (latest available Office for National Statistics (ONS) unit-based data). The program consists of five elements: training, evidence-based guidelines for risk assessment and surveillance of fetal growth, customized charts, recording of process and outcome indicators, and audit of missed SGA cases. All maternity units in England were categorized into one of three groups according to their GAP status in 2017: (1) not in the GAP program; (2) GAP implemented partially (incomplete adoption of protocol, no monitoring and audit); and (3) GAP implemented completely. A subset of the complete-implementation group comprised the 20 units with the highest SGA detection rates. Unit-level live-birth and stillbirth data were obtained from the ONS for each of these groups., Results: Stillbirth rates declined across all groups from 2008 to 2017, and significantly more in units in which GAP was implemented completely than in the non-GAP units (P < 0.05). The steepest decline in stillbirth rate was observed in the 20 units with the highest SGA detection rates, which had a 24% lower stillbirth rate compared with the units not using GAP (P < 0.01) in 2017. This difference remained significant after mixed-effects logistic regression analysis of potential confounding, including social deprivation (odds ratio, 0.76 (95% CI, 0.64-0.90)). Assessment of the nine Bradford Hill causality criteria and associated characteristics suggested that the association between implementation of the GAP program and reduction in stillbirth rate was causal., Conclusions: There has been an overall reduction in stillbirth rates in England that is likely to be a result of increased awareness of the importance of antenatal detection of SGA as a key risk factor for stillbirth. The decline in stillbirth rates was significantly greater in maternity units that had fully implemented the GAP program, and was most pronounced in the units with the highest antenatal SGA detection rates. © 2020 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology., (© 2020 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.)

Objective: To define cut-off limits for individually adjustable fetal weight standards for the detection of intrauterine growth restriction., Design: Retrospective study, with the outcome measures small-for-gestational age (SGA) birth weight, operative delivery for fetal distress, umbilical artery pH < 7.15, and admission to the neonatal intensive care unit., Subjects and Methods: Two hundred and fifteen women considered to be at increased risk of uteroplacental insufficiency were recruited to a study of serial ultrasound scans. Fetal weights were derived using standard formulae and, retrospectively, weight percentiles were calculated after individual adjustment for maternal height, weight in early pregnancy, ethnic group, parity and fetal sex., Introduction: One or more antenatal scans indicative of fetal weight below the 10th customized percentile were predictive for a SGA neonate at birth (P < 0.001), operative delivery for fetal distress (P < 0.01) and admission to neonatal intensive care (P < 0.01) but not for a low umbilical artery pH (P = 0.6). Receiver-operator curves showed the optimal customized fetal weight percentile limit for predicting an SGA neonate to be the 18th percentile (sensitivity 83%, specificity 79%, positive predictive value 63% and negative predictive value 92%). For the prediction of operative delivery for fetal distress and admission to neonatal intensive care, the optional customized cut-off value was the 8th percentile., Conclusions: The assessment of fetal weight using ultrasound and an individually-adjusted standard is predictive of growth restriction and perinatal events associated with hypoxia or diminished reserve. The optimal cut-off value for predicting operative delivery for fetal distress or admission to the neonatal intensive care unit suggests that the 10th customized percentile is a good limit for clinical use.

Objective: To study fetal weight gain and its association with adverse perinatal events in a serially scanned high-risk population., Subjects and Methods: A total of 200 pregnant women considered at increased risk of uteroplacental insufficiency had a total of 1140 scans in the third trimester, with a median of six scans in each pregnancy. The average fetal growth rate was retrospectively calculated for the last 6 weeks to birth, and expressed as daily weight gain in grams per day. Adverse pregnancy outcome was defined as operative delivery for fetal distress, acidotic umbilical artery pH (< 7.15), or admission to the neonatal intensive care unit (NICU)., Results: Fetuses with normal outcome in this high-risk pregnancy population had an average antenatal growth rate of 24.2 g/day. Compared to pregnancies with normal outcome, the growth rate was slower in those that required operative delivery for fetal distress (20.9 g/day, p < 0.05) and those that required admission to the NICU (20.3 g/day, p < 0.05). The growth rate in pregnancies resulting in acidotic umbilical artery pH also seemed lower, but this did not reach statistical significance., Conclusions: Impaired fetal weight gain prior to birth is associated with adverse perinatal events suggestive of growth failure.

Physiological as well as pathological variables influence fetal growth. This study was undertaken to assess the influence of physiological variables on fetal weight gain in a high-risk population with normal outcome. A total of 121 pregnancies had 3-13 (median 8) ultrasound scans in the third trimester. Estimated fetal weight was calculated according to standard formulae. The estimated fetal weight at 30, 34 and 38 weeks and growth per day in the last 2 weeks prior to delivery were calculated and compared between subgroups defined on physiological characteristics, such as maternal height, maternal weight, parity and fetal sex. There were differences in growth curves for each of the physiological parameters studied. Maternal height and weight were significantly related to the estimated fetal weight throughout the third trimester but there were no significant differences in growth per day in the last 2 weeks before birth. In contrast, subgroups defined by parity and fetal sex did not show significant fetal weight differences in the third trimester, but the daily growth rate prior to birth was significantly higher for multiparae and male fetuses. Physiological factors affect fetal weight gain and need to be taken into account when fetal growth is monitored in high-risk pregnancies.

A dataset of 64 pregnancies conceived by artificial reproductive techniques was studied to assess the accuracy of second-trimester dating formulae when these were applied in routine ultrasound clinics in different centers. Dating formulae for biparietal diameter (BPD) and femur length (FL) were derived for a gestational age range of 14-23 weeks. The best fit curves represented linear equations: gestational age (days) = 44.2 + 2 x BPD; and gestational age (days) = 67.4 + 2.3 x FL. Twelve published formulae for biparietal diameter and femur length were reviewed and systematic and random errors were calculated for these formulae when they were applied to second-trimester scan measurements in precisely dated pregnancies. Overall, published dating formulae performed well in predicting gestational age. The 95% confidence interval was 8.3 days for biparietal diameter and 10.2 days for femur length. The study confirms the accuracy of ultrasound dating in routine ultrasound clinics and supports the use of ultrasound measurement alone in preference to menstrual history for dating pregnancy.

We investigated fetal weight gain in relation to maternal characteristics within a normal, heterogeneous population in Nottingham, UK. A total of 226 low-risk pregnancies with normal neonatal outcome were examined longitudinally by serial ultrasound examination. Gestation was calculated from early measurements of biparietal diameter. A modified Hadlock's formula for fetal weight was employed, using the biparietal diameter, abdominal circumference and femur length, which was not associated with any significant systematic error. Individual curves were obtained by fitting serial fetal weight estimates and birth weight in a weighted log-polynomial model for fetal growth. The overall growth formula showed an almost linear relationship between gestational age and fetal weight at term. Maternal height and weight at the first hospital visit were positively correlated with fetal weight in the third trimester. The fetuses of parous women were also heavier in late pregnancy, as were those of European compared to Indo-Pakistani mothers. Intrauterine weight gain in the third trimester shows variation with pregnancy characteristics which need to be considered when fetal growth is assessed.

The monitoring of fetal weight is an important aspect of antenatal care. To construct an individually adjustable standard, we developed a model to link the predicted birth weight to a fetal weight curve which outlines how this weight is to be reached in an uncomplicated pregnancy. A formula was derived which describes the median fetal weight at each gestation as a proportion of the optimal term weight, and also defines the 90th and 10th centile curves as normal limits. We analyzed a birth weight database of 38,114 singleton, routine ultrasound-dated pregnancies resulting in term deliveries. By stepwise multiple regression analysis, we derived coefficients for the factors that act as variables on term birth weight in our population. Apart from gestational age and sex, the maternal height, weight at first visit, ethnic group, parity and smoking all have significant and independent effects on birth weight. The variation due to ethnic group appears to be physiological in this population. Smoking is associated with a reduction in birth weight, which is independent of maternal physique and related to the number of cigarettes per day as reported at the first visit. We have developed a software program which calculates, on the basis of pregnancy variables entered at the first visit, an adjusted normal range for fetal size. This can be printed out as a chart and used for antenatal surveillance of growth.