Fetal growth in Peru: comparisons with international fetal size charts and implications for fetal growth assessment

The choice of reference chart affects the strength of the association between malaria in pregnancy and small for gestational age: an individual participant data meta-analysis comparing the Intergrowth-21 with a Tanzanian birthweight chart

BACKGROUND

The prevalence of small for gestational age (SGA) may vary depending on the chosen weight-for-gestational-age reference chart. An individual participant data meta-analysis was conducted to assess the implications of using a local reference (STOPPAM) instead of a universal reference (Intergrowth-21) on the association between malaria in pregnancy and SGA.

METHODS

Individual participant data of 6,236 newborns were pooled from seven conveniently identified studies conducted in Tanzania and Malawi from 2003-2018 with data on malaria in pregnancy, birthweight, and ultrasound estimated gestational age. Mixed-effects regression models were used to compare the association between malaria in pregnancy and SGA when using the STOPPAM and the Intergrowth-21 references, respectively.

RESULTS

The 10th percentile for birthweights-for-gestational age was lower for STOPPAM than for Intergrowth-21, leading to a prevalence of SGA_STOPPAM of 14.2% and SGA_IG21 of 18.0%, p < 0.001. The association between malaria in pregnancy and SGA was stronger for STOPPAM (adjusted odds ratio (aOR) 1.30 [1.09-1.56], p < 0.01) than for Intergrowth-21 (aOR 1.19 [1.00-1.40], p = 0.04), particularly among paucigravidae (SGA_STOPPAM aOR 1.36 [1.09-1.71], p < 0.01 vs SGA_IG21 aOR 1.21 [0.97-1.50], p = 0.08).

CONCLUSIONS

The prevalence of SGA may be overestimated and the impact of malaria in pregnancy underestimated when using Intergrowth-21. Comparing local reference charts to global references when assessing and interpreting the impact of malaria in pregnancy may be appropriate.

Which fetal growth charts should be used? A retrospective observational study in China

BACKGROUND

The fetal growth charts in widest use in China were published by Hadlock >35 years ago and were established on data from several hundred of American pregnant women. After that, >100 fetal growth charts were published around the world. We attempted to assess the impact of applying the long-standing Hadlock charts and other charts in a Chinese population and to compare their ability to predict newborn small for gestational age (SGA).

METHODS

For this retrospective observational study, we reviewed all pregnant women ( n  = 106,455) who booked prenatal care with ultrasound measurements for fetal biometry at the Shenzhen Maternity and Child Healthcare Hospital between 2012 and 2019. A fractional polynomial regression model was applied to generate Shenzhen fetal growth chart ranges for head circumference (HC), biparietal diameter (BPD), abdominal circumference (AC), and femur length (FL). The differences between Shenzhen charts and published charts were quantified by calculating the Z -score. The impact of applying these published charts was quantified by calculating the proportions of fetuses with biometric measurements below the 3rd centile of these charts. The sensitivity and area under the receiver operating characteristic curves of published charts to predict neonatal SGA (birthweight <10th centile) were assessed.

RESULTS

Following selection, 169,980 scans of fetal biometry contributed by 41,032 pregnancies with reliable gestational age were analyzed. When using Hadlock references (<3rd centile), the proportions of small heads and short femurs were as high as 8.9% and 6.6% in late gestation, respectively. The INTERGROWTH-21st standards matched those of our observed curves better than other charts, in particular for fat-free biometry (HC and FL). When using AC<10th centile, all of these references were poor at predicting neonatal SGA.

CONCLUSIONS

Applying long-standing Hadlock references could misclassify a large proportion of fetuses as SGA. INTERGROWTH-21st standard appears to be a safe option in China. For fat-based biometry, AC, a reference based on the Chinese population is needed. In addition, when applying published charts, particular care should be taken due to the discrepancy of measurement methods.

Fetal biometric parameters: Reference charts for a non-selected risk population from Uberaba, Brazil

OBJECTIVE

To establish reference charts for fetal biometric parameters in a non-selected risk population from Uberaba, Southeast of Brazil.

METHODS

A retrospective cross-sectional study was performed among 5656 non-selected risk singleton pregnant women between 14 and 41 weeks of gestation. The ultrasound exams were performed during routine visits of second and third trimesters. Biparietal diameter (BPD) was measured at the level of the thalami and cavum septi pellucidi. Head circumference (HC) was calculated by the following formula: HC = 1.62*(BPD + occipital frontal diameter, OFD). Abdominal circumference (AC) was measured using the following formula: AC = (anteroposterior diameter + transverse abdominal diameter) × 1.57. Femur diaphysis length (FDL) was obtained in the longest axis of femur without including the distal femoral epiphysis. The estimated fetal weight (EFW) was obtained by the Hadlock formula. Polynomial regressions were performed to obtain the best-fit model for each fetal biometric parameter as the function of gestational age (GA).

RESULTS

The mean, standard deviations (SD), minimum and maximum of BPD (cm), HC (cm), AC (cm), FDL (cm) and EFW (g) were 6.9 ± 1.9 (2.3 - 10.5), 24.51 ± 6.61 (9.1 - 36.4), 22.8 ± 7.3 (7.5 - 41.1), 4.9 ± 1.6 (1.2 - 8.1) and 1365 ± 1019 (103 - 4777), respectively. Second-degree polynomial regressions between the evaluated parameters and GA resulted in the following formulas: BPD = -4.044 + 0.540 × GA - 0.0049 × GA² (R² = 0.97); HC= -15.420 + 2.024 GA - 0.0199 × GA² (R² = 0.98); AC = -9.579 + 1.329 × GA - 0.0055 × GA² (R² = 0.97); FDL = -3.778 + 0.416 × GA - 0.0035 × GA² (R² = 0.98) and EFW = 916 - 123 × GA + 4.70 × GA² (R² = 0.96); respectively.

CONCLUSION

Reference charts for the fetal biometric parameters in a non-selected risk population from Uberaba, Southeast of Brazil, were established.

Scientific basis for standardization of fetal head measurements by ultrasound: a reproducibility study

OBJECTIVE

To compare the standard methods for ultrasound measurement of fetal head circumference (HC) and biparietal diameter (BPD) (outer-to-outer (BPDoo) vs outer-to-inner (BPDoi) caliper placement), and compare acquisition of these measurements in transthalamic (TT) vs transventricular (TV) planes.

METHODS

This study utilized ultrasound images acquired from women participating in the Oxford arm of the INTERGROWTH-21(st) Project. In the first phase of the study, BPDoo and BPDoi were measured on stored images. In the second phase, real-time measurements of BPD, occipitofrontal diameter (OFD) and HC in TT and TV planes were obtained by pairs of sonographers. Reproducibility of measurements made by the same (intraobserver) and by different (interobserver) sonographers, as well as the reproducibility of caliper placement and measurements obtained in different planes, was assessed using Bland-Altman plots.

RESULTS

In Phase I, we analyzed ultrasound images of 108 singleton fetuses. The mean intraobserver and interobserver differences were < 2% (1.34 mm) and the 95% limits of agreement were < 5% (3 mm) for both BPDoo and BPDoi. Neither method for measuring BPD showed consistently better reproducibility. In Phase II, we analyzed ultrasound images of 100 different singleton fetuses. The mean intraobserver and interobserver differences were < 1% (2.26 mm) and the 95% limits of agreement were < 8% (14.45 mm) for all fetal head measurements obtained in TV and TT planes. Neither plane for measuring fetal head showed consistently better reproducibility. Measurement of HC using the ellipse facility was as reproducible as HC calculated from BPD and OFD. OFD by itself was the least reproducible of all fetal head measurements.

CONCLUSIONS

Measurements of BPDoi and BPDoo are equally reproducible; however, we believe BPDoo should be used in clinical practice as it allows fetal HC to be measured and compared with neonatal HC. For all head measurements, TV and TT planes provide equally reproducible values at any gestational age, and HC values are similar in both planes. Fetal head measurement in the TT plane is preferable as international standards in this plane are available; however, measurements in the TV plane can be plotted on the same standards. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

National curves of foetal growth in singleton foetuses of Greek origin

BACKGROUND

Foetal growth monitoring is an essential component of prenatal care with postnatal impact. The aim of the study was to construct reference ranges for foetal biometric parameters in Greek foetuses and to compare them with previously published models.

MATERIALS AND METHODS

Measurements from 1200 Greek foetuses were used to construct normal curves for biparietal diameter (BPD), occipitofrontal diameter (OFD), head circumference (HC), abdominal circumference (AC), femoral length (FL) and the BPD/FL ratio according to the methodology described by Royston and Wright (1998). The model was validated in a second group of 1200 different foetuses using analysis of the corresponding standardized residuals (z-scores). The z-scores which were derived by our model were compared to those calculated using previously published models from other populations.

RESULTS

BPD, OFD, HC, AC, FL and the BPD/FL ratio are accurately described by simple quadratic equations (R(2) > 0·96 for most of the parameters tested). Statistically significant differences were observed for most of the z-scores when our models were compared to previously published models. Less than 10% of our foetuses were < 5th or > 95th centile of the latter models. About 10% of our foetuses were > 95th centile for FL and HC when the INTERGROWTH-21st formulas were used.

CONCLUSION

We present national foetal biometric references. Using charts from other populations (including INTERGROWTH-21st) may be unrepresentative of local populations and lead to misclassification of foetal growth status.

Improving customized fetal biometry by longitudinal modelling

OBJECTIVE

To develop customized biometric charts to better define abnormal fetal growth.

METHODS

A total of 1056 singleton fetuses from the Raine Study underwent serial ultrasound biometry (abdominal circumference [AC], head circumference, and femur length) at 18, 24, 28, 34, and 38 weeks' gestation. Customized biometry trajectories were developed adjusting for epidemiological influences upon fetal biometry using covariates available at 18 weeks gestation. Prediction accuracy (areas under the receiver operating characteristic curve [AUC] and 95% confidence interval [95%CI]) was evaluated by repeated random sub-sampling cross-validation methodology.

RESULTS

The model for derived estimated fetal weight (EFW) performed well for EFW less than 10th predicted percentile (AUC = 0.695, 95%CI, 0.692-0.699) and EFW greater than 90th predicted percentile (AUC = 0.705, 95%CI, 0.702-0.708). Fetal AC was also well predicted for growth restriction (AUC = 0.789, 95%CI, 0.784-0.794) and macrosomia (AUC = 0.796, 95%CI, 0.793-0.799). Population-derived, sex-specific charts misclassified 7.9% of small fetuses and 10.7% of large fetuses as normal. Conversely, 9.2% of those classified as abnormally grown by population-derived charts were considered normal by customized charts, potentially leading to complications of unnecessary intervention.

CONCLUSIONS

Customized fetal biometric charts may offer improved ability for clinicians to detect deviations from optimal fetal growth and influence pregnancy management.

Unconditional and conditional standards for fetal abdominal circumference and estimated fetal weight in an ethnic Chinese population: a birth cohort study

BACKGROUND

Diagnosis of intrauterine fetal growth restriction and prediction of small-for-gestation age are often based on fetal abdominal circumference or estimated fetal weight (EFW). The present study aims to create unconditional (cross-sectional) and conditional (longitudinal) standards of fetal abdominal circumference and EFW for use in an ethnic Chinese population.

METHODS

In the Growing Up in Singapore Towards healthy Outcome (GUSTO) birth cohort study in Singapore, fetal biometric measurements were obtained at enrolment to antenatal care (11-12 weeks) and up to three more time points during pregnancy. Singleton pregnancies with a healthy profile defined by maternal, pregnancy and fetal characteristics and birth outcomes were selected for this analysis. The Hadlock algorithm was used to calculate EFW. Mixed effects model was used to establish unconditional and conditional standards in z-scores and percentiles for both genders pooled and for each gender separately.

RESULTS

A total of 313 women were included, of whom 294 had 3 and 19 had 2 ultrasound scans other than the gestational age dating scan. Fetal abdominal circumference showed a roughly linear trajectory from 18 to 36 weeks of gestation, while EFW showed an accelerating trajectory. Gender differences were more pronounced in the 10(th) percentile than the 50(th) or 90(th) percentiles. As compared to other published charts, this population showed growth trajectories that started low but caught up at later gestations.

CONCLUSIONS

Unconditional and conditional standards for monitoring fetal size and fetal growth in terms of abdominal circumference and EFW are available for this ethnic-Chinese population. Electronic spreadsheets are provided for their implementation.

Fetal size in a rural melanesian population with minimal risk factors for growth restriction: an observational ultrasound study from Papua New Guinea

We conducted a prospective longitudinal study of fetal size in rural Papua New Guinea (PNG) involving 439 ultrasound-dated singleton pregnancies with no obvious risk factors for growth restriction. Sonographically estimated fetal weights (EFWs; N = 788) and birth weights (N = 376) were included in a second-order polynomial regression model (optimal fit) to generate fetal weight centiles. Means for specific fetal biometric measurements were also estimated. Fetal weight centiles from a healthy PNG cohort were consistently lower than those derived from Caucasian and Congolese populations, which overestimated the proportion of fetuses measuring small for gestational age (SGA; < 10th centile). Tanzanian and global reference centiles (Caucasian weight reference adapted to our PNG cohort) were more similar to those observed in our cohort, but the global reference underestimated SGA. Individual biometric measurements did not differ significantly from other cohorts. In rural PNG, a locally derived nomogram may be most appropriate for detection of SGA fetuses.

WHO multicentre study for the development of growth standards from fetal life to childhood: the fetal component

Background

In 2006 WHO presented the infant and child growth charts suggested for universal application. However, major determinants for perinatal outcomes and postnatal growth are laid down during antenatal development. Accordingly, monitoring fetal growth in utero by ultrasonography is important both for clinical and scientific reasons. The currently used fetal growth references are derived mainly from North American and European population and may be inappropriate for international use, given possible variances in the growth rates of fetuses from different ethnic population groups. WHO has, therefore, made it a high priority to establish charts of optimal fetal growth that can be recommended worldwide.

Methods

This is a multi-national study for the development of fetal growth standards for international application by assessing fetal growth in populations of different ethnic and geographic backgrounds. The study will select pregnant women of high-middle socioeconomic status with no obvious environmental constraints on growth (adequate nutritional status, non-smoking), and normal pregnancy history with no complications likely to affect fetal growth. The study will be conducted in centres from ten developing and industrialized countries: Argentina, Brazil, Democratic Republic of Congo, Denmark, Egypt, France, Germany, India, Norway, and Thailand. At each centre, 140 pregnant women will be recruited between 8 + 0 and 12 + 6 weeks of gestation. Subsequently, visits for fetal biometry will be scheduled at 14, 18, 24, 28, 32, 36, and 40 weeks (+/− 1 week) to be performed by trained ultrasonographers.

The main outcome of the proposed study will be the development of fetal growth standards (either global or population specific) for international applications.

Discussion

The data from this study will be incorporated into obstetric practice and national health policies at country level in coordination with the activities presently conducted by WHO to implement the use of the Child Growth Standards.

Development of a fetal weight chart using serial trans-abdominal ultrasound in an East African population: a longitudinal observational study

Objective

To produce a fetal weight chart representative of a Tanzanian population, and compare it to weight charts from Sub-Saharan Africa and the developed world.

Methods

A longitudinal observational study in Northeastern Tanzania. Pregnant women were followed throughout pregnancy with serial trans-abdominal ultrasound. All pregnancies with pathology were excluded and a chart representing the optimal growth potential was developed using fetal weights and birth weights. The weight chart was compared to a chart from Congo, a chart representing a white population, and a chart representing a white population but adapted to the study population. The prevalence of SGA was assessed using all four charts.

Results

A total of 2193 weight measurements from 583 fetuses/newborns were included in the fetal weight chart. Our chart had lower percentiles than all the other charts. Most importantly, in the end of pregnancy, the 10^th percentiles deviated substantially causing an overestimation of the true prevalence of SGA newborns if our chart had not been used.

Conclusions

We developed a weight chart representative for a Tanzanian population and provide evidence for the necessity of developing regional specific weight charts for correct identification of SGA. Our weight chart is an important tool that can be used for clinical risk assessments of newborns and for evaluating the effect of intrauterine exposures on fetal and newborn weight.

Measurements using 7.0 T post-mortem magnetic resonance imaging of the scalar dimensions of the fetal brain between 12 and 20 weeks gestational age

In this study, scalar values for the fetal brain from 12 to 20 weeks gestational age were obtained. Fifty-two fetal specimens of 12-20 weeks gestational age with an anatomically normal and developmentally appropriate central nervous system (CNS) were scanned using a 7.0 T magnetic resonance imaging (MRI) scanner. The linear biometric measurements of the brain were then determined. All the measurements (except for the interhemispheric distance) were found to increase linearly with gestational age, although each increased at a different growth rates. The 95% confidence interval for each value was obtained. These data may be considered to be a valuable reference for the assessment of normal fetal brain development in clinical settings and as a supplement to post-mortem MRI or anatomical investigations.

Defining normal and abnormal fetal growth: promises and challenges

Normal fetal growth is a critical component of a healthy pregnancy and influences the long-term health of the offspring. However, defining normal and abnormal fetal growth has been a long-standing challenge in clinical practice and research. We review various references and standards that are used widely to evaluate fetal growth and discuss common pitfalls of current definitions of abnormal fetal growth. Pros and cons of different approaches to customize fetal growth standards are described. We further discuss recent advances toward an integrated definition for fetal growth restriction. Such a definition may incorporate fetal size with the status of placental health that is measured by maternal and fetal Doppler velocimetry and biomarkers, biophysical findings, and genetics. Although the concept of an integrated definition appears promising, further development and testing are required. An improved definition of abnormal fetal growth should benefit both research and clinical practice.

Measurement error for ultrasound fetal biometry performed by paramedics in rural Bangladesh

OBJECTIVES

To document the accuracy and precision of sonographic fetal biometry performed by nine paramedics from rural Bangladesh.

METHODS

Paramedics underwent intensive training (6 weeks) including hands-on practice then underwent a series of standardization exercises. Measurements of each fetus were taken by a highly-trained medical doctor (study supervisor) and the nine paramedics. Crown-rump length (CRL) in fetuses of less than 10 weeks' gestation, and biparietal diameter (BPD), occipitofrontal diameter, head and abdominal circumference (AC) and femur diaphysis length (FL) were measured twice using standard procedures by each paramedic and the medical doctor for each fetus, with at least 20 min between them. Precision was quantified using variance components analysis; the intraobserver error for each of the paramedics was calculated by comparing repeat measurements taken on the same participant, and the measurements obtained by each individual paramedic were also compared with those taken by the others (interobserver error). Accuracy was estimated by comparing the mean of the two measures taken by each paramedic to those taken by the study supervisor using paired t-tests. Bland-Altman plots were used to visually assess the relationship between precision of repeat measurements (intraobserver error) and fetal size.

RESULTS

A total of 180 women, at 7 to 31 weeks' gestation, participated in the study. Intraobserver error of the measurements obtained by the paramedics, expressed as the mean SD, ranged from 0.97 mm for BPD in the first trimester to 7.25 mm for AC in the third trimester, and was larger than the interobserver error (i.e. accounting for a greater proportion of total variance) for most measurements. Interobserver error ranged from 0.00 mm for FL to 3.36 mm for AC, both in the third trimester. For all measurements except CRL, intraobserver error increased with increasing fetal size. The measurements obtained by the paramedics did show some statistically significant differences from those obtained by the study supervisor, but these were relatively small in magnitude.

CONCLUSIONS

Both inter- and intraobserver measurement errors were within the range reported in the literature for studies conducted by technical staff and medical doctors. With intense training, paramedics with no prior exposure to ultrasonography can provide accurate and precise measures of fetal biometry.