Birth weight prediction from remote ultrasonographic examination

Comparing INTERGROWTH-21st Century and Hadlock growth standards to predict small for gestational age and short-term neonatal outcomes

Objective: To compare the INTERGROWTH-21st Century growth standard to the Hadlock standard in predicting small for gestational age (SGA) and adverse neonatal outcomes.Method: This is a prospective cohort study on women with singleton gestations referred for fetal growth ultrasound between 26.0 and 36.6 weeks gestational age (GA). The primary outcome is prediction of neonatal SGA. Neonatal SGA was defined as birthweight <10th percentile for GA by Alexander chart. The discriminatory ability of the growth standards was compared using area under receiver operating characteristic curves (AUC).Results: Among 1054 patients who met inclusion criteria, 139 (13.2%) had neonatal SGA. The mean interval between estimated fetal weight and birthweight was 6.7 ± 3.1 weeks. Composite adverse neonatal outcome was seen in 300 (28.4%) patients. The sensitivity for identifying SGA neonates was higher for Hadlock compared with INTERGROWTH-21st standard (41.7 vs. 24.5%); AUC (95% CI) were 0.69 (0.65-0.73) and 0.62 (0.58-0.65), respectively. Both standards were comparable in predicting the composite adverse neonatal outcomes; AUC (95% CI) were 0.52 (0.50-0.53) and 0.52 (0.50-0.54), respectively; p = .28.Conclusions: The Hadlock standard had a moderate but higher discriminatory ability for predicting neonatal SGA compared to the INTERGROWTH-21st project standard. However, the two standards were poor predictors of early adverse neonatal outcomes.Rationale: The Intergrowth-21st project was recently introduced with the goal of providing a universal benchmark for comparing growth across different ethnicity. We performed a prospective cohort study to compare the Intergrowth-21st standard with the commonly used Hadlock standard for predicting pregnancies at risk for neonatal SGA and adverse outcomes. Hadlock fetal growth standard is moderately superior at predicting neonatal SGA compared to the Intergrowth-21st standard. Both standards are poor at predicting adverse neonatal outcomes. These findings, however, need further validation.

Prospective assessment of INTERGROWTH-21st and World Health Organization estimated fetal weight reference curves

OBJECTIVES

To assess the suitability of the new INTERGROWTH-21^st and World Health Organization (WHO) estimated fetal weight (EFW) references in a Southern Chinese population. A secondary aim was to determine the accuracy of EFW by assessing the difference between EFW and actual birth weight.

METHODS

This was a prospective cross-sectional cohort study. Viable singleton pregnancies at 11-13 weeks' gestation were recruited to undergo a single standardized fetal biometric scan after 20 weeks. The gestational age at which the scan was performed was allocated randomly at the time of recruitment. EFW was predicted using both the Hadlock and INTERGROWTH-21^st weight estimation model formulae. Population-specific EFW references were constructed. Z-scores were used to compare these references against the INTERGROWTH-21^st and WHO international size references. Gestational-age-adjusted projection was used to assess the difference between EFW on the day of delivery and birth weight for fetuses having biometry scans ≥ 34 weeks.

RESULTS

Fetuses of 970 participants had biometry scans. The median number of scans per gestational week was 48 (interquartile range, 43-53). Z-score comparison indicated that the WHO 10^th , 50^th and 90^th centiles of the EFW reference were consistently higher than the corresponding local centiles, whilst the INTERGROWTH-21^st 10^th centile was lower. Fewer than 2% of fetuses scanned at or after 34 weeks would be considered as potentially large-for-gestational age, irrespective of which model was used to predict weight. Adopting the WHO international reference would result in approximately one in six fetuses being regarded as potentially small-for-gestational age, 50% more than the number determined using a population-specific reference. Systematic errors of extrapolated EFW were similar, ranging from 5.5% to 7.4%.

CONCLUSIONS

Centers seeking to use new references, such as the INTERGROWTH-21^st and/or WHO international references, as a means of determining whether a fetus is small- or large-for-gestational age, would be advised to assess the suitability of these references within their own population using standardized methodology. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Fetal growth cessation in late pregnancy: its impact on predicted size parameters used to classify small for gestational age neonates

OBJECTIVE

To evaluate the impact of late 3rd trimester fetal growth cessation on anatomical birth characteristic predictions used in classifying SGA neonates.

METHODS

A prospective longitudinal study was performed in 119 pregnancies with normal neonatal growth outcomes. Seven biometric parameters were measured at 3-4 weeks intervals using 3D ultrasonography. Rossavik size models were determined to predict birth characteristics at different ages. Percent Differences (% Diff) were calculated from predicted and measured birth characteristics. Growth Cessation Ages (GCA) were identified when no systematic change in % Diff values occurred after specified prediction ages. Systematic and random prediction errors were compared using different assumptions about the GCA. Predicted and measured size parameters were used to determine six new Growth Potential Realization Index (GPRI) reference ranges. Five were used to sub-classify 34 SGA neonates (weight < 10th percentile) based on the number of abnormal GPRI values.

RESULTS

Growth cessation ages were 38 weeks for HC, AC, mid-thigh circumference, estimated weight and mid-arm circumference. Crown-heel length GCA was 38.5 weeks. At GCA, birth characteristics had prediction errors that varied from 0.08 ± 3.4% to 15.7 ± 9.1% and zero % Diff slopes after 38 weeks. Assuming growth to delivery gave increased systematic and random prediction errors as well as positive % Diff slopes after 38 weeks, MA. Seventeen of the SGA neonates had 0 or 1 abnormal GPRI values [Subgroup 1] and 17 others had 2 or more abnormal values [Subgroup 2]. In Subgroup 1, 4/85 (4.7%) of GPRI's were abnormal while in Subgroup 2, 43/85 (50.6%) were abnormal. Use of only one type of GPRI for SGA subclassification resulted in substantial false negative and some false positive rates when compared to subclassification based on all five GPRI values.

CONCLUSIONS

Growth cessation occurred at approximately 38 weeks for all six birth characteristics studied. SGA neonates can be separated into normal and growth restricted subgroups based on the frequency of abnormal GPRI values (GPRI Profile Classification).

Accuracy of sonographic prediction of birth weight

Many clinicians use ultrasound estimates of fetal weight to assess fetal growth. This study assessed the accuracy of the Hadlock IV equation, the equation used at the Royal Hospital for Women, Randwick, NSW, in estimating birth weight. The accuracy of the Hadlock IV equation was assessed based on systematic and random error as well as absolute error. 709 women who underwent ultrasound examination within 8 weeks of delivery between January 2009-May 2011 were included. 305 women underwent ultrasound less than 2 weeks before delivery. The systematic, random and absolute errors of the Hadlock IV equation were -0.47, 27.45 and 8.52%, respectively. This study demonstrates that clinicians may rely on ultrasound estimates of fetal weight performed by well-trained staff in a tertiary institution within 2 weeks of delivery. The accuracy diminishes as the interval between testing and delivery increases. Absolute errors tended to increase with increasing birth weight for all ultrasound-delivery intervals.

Improved ultrasonographic estimation of birth weight in macrosomic fetuses by application of a correction factor to the gestation-adjusted projection method

OBJECTIVE

The purpose of this study was to improve estimated birth weight (EBW) determination in macrosomic fetuses (estimated fetal weight >or=4000 g) by application of a correction factor to the gestation-adjusted projection (GAP) method.

METHODS

A review was performed of 411 singleton pregnancies delivered at term. On the basis of ultrasonographic examinations previously performed between 34.0 and 36.9 weeks' gestation, an EBW was calculated for each patient by the GAP method (EBW(GAP)). Using linear regression, a correction factor was developed that minimized the systematic error in the EBW(GAP). The model was then tested retrospectively on a second group of 317 patients.

RESULTS

The GAP method systematically overestimated weights of the heavier fetuses in our population. The model we derived showed improved accuracy compared with the GAP method. When applied to a second group of 317 patients, our correction to the GAP method improved specificity for macrosomia from 94.7% to 98.6% (P = .003). Stated differently, the false-positive rate was reduced from 5.3% to 1.4%. The difference in sensitivity for macrosomia was not significant: 41.2% and 35.3% (P = .68).

CONCLUSIONS

Application of our model to our study population reduced the number of false-positive results for fetal macrosomia.

Menstrual age-dependent systematic error in sonographic fetal weight estimation: a mathematical model

PURPOSE

We used computer modeling techniques to evaluate the accuracy of different types of sonographic formulas for estimating fetal weight across the full range of clinically important menstrual ages.

METHODS

Input data for the computer modeling techniques were derived from published British standards for normal distributions of sonographic biometric growth parameters and their correlation coefficients; these standards had been derived from fetal populations whose ages were determined using sonography. The accuracy of each of 10 formulas for estimating fetal weight was calculated by comparing the weight estimates obtained with these formulas in simulated populations with the weight estimates expected from birth weight data, from 24 weeks' menstrual age to term. Preterm weights were estimated by interpolation from term birth weights using sonographic growth curves. With an ideal formula, the median weight estimates at term should not differ from the population birth weight median.

RESULTS

The simulated output sonographic values closely matched those of the original population. The accuracy of the fetal weight estimation differed by menstrual age and between various formulas. Most methods tended to overestimate fetal weight at term. Shepard's formula progressively overestimated weights from about 2% at 32 weeks to more than 15% at term. The accuracy of Combs's and Shinozuka's volumetric formulas varied least by menstrual age. Hadlock's formula underestimated preterm fetal weight by up to 7% and overestimated fetal weight at term by up to 5%.

CONCLUSIONS

The accuracy of sonographic fetal weight estimation based on volumetric formulas is more consistent across menstrual ages than are other methods.

Estimating fetal weight in the management of macrosomia

The purpose of this review is to examine the evidence that, including estimates of fetal macrosomia in patient care, will decrease adverse perinatal outcomes. A literature search for the years 1980 to 1999 was used. Shoulder dystocia and brachial plexus injuries occur more often in macrosomic than in non-macrosomic neonates. However, 26 to 58 percent of shoulder dystocias and 24 to 44 percent of brachial plexus injuries occur to babies weighing less than 4000 gm. Persistence of impairment is extremely rare. Neither historical nor clinical factors have strong positive predictive values for macrosomia. From 15 to 81 percent of the babies predicted to be macrosomic are confirmed by birth weight. Of babies determined to be macrosomic at birth, only 50 to 100 percent were successfully predicted. Shoulder dystocia and brachial plexus injuries are unpredictable events. Available evidence suggests that planned interventions based on estimates of fetal weight do not reduce the incidence of shoulder dystocia and do not decrease adverse outcomes attributable to fetal macrosomia.

Sonographic diagnosis of intrauterine growth restriction

Estimation of fetal weight in utero using multiple ultrasonic parameters remains the mainstay in screening for IUGR. The use of various fetal morphometric ratios and/or measurements of other fetal parameters may provide additional useful information. Serial evaluation to assess interval growth may be necessary to clarify the diagnosis. The use of Doppler ultrasound, especially the evaluation of the umbilical artery and middle cerebral artery velocity flow, is an important adjunct for both the diagnosis of IUGR caused by uteroplacental insufficiency and its continued management.

Ultrasound fetal weight estimation: precision or guess work?

We compared the prediction of birth-weight based on factors shown by epidemiological studies to influence it with the performance of 2 clinical examples of ultrasonic fetal weight estimation reported in the literature. The standardized absolute error of the 2 examples of ultrasonic fetal weight estimation was similar to estimation by multiple regression of birth-weight on maternal age, parity, height and weight in 11,516 Chinese mothers. This severely limits the clinical utility of the estimation derived from these ultrasonic measurements.

Ultrasonographic fetal weight estimation by an integrated computer-assisted system: can each laboratory improve its accuracy?

Estimated fetal weights from 1684 cases with singleton, live infants born within 7 days of an ultrasonographic examinations were compared with their birth weights, which ranged from 520 to 5920 gm. Estimated weight calculated from Shepard's equation produced a linear relationship of birth weight against estimated weight with an intercept and slope of 209.5 gm and 0.929. Overall, 75% of the estimated weights were within 15% of the actual weight. A separate regression model that used the same variables from Shepard's equation failed to improve the comparison between estimated and actual weights. All cases were reevaluated with multiple regression modeling. Various examination-to-birth intervals were analyzed; intervals less than or equal to 3 days appeared optimal. The best equation increased the percent of cases that were within 15% of the actual birth weight to 80%. The plot of birth weight against estimated weight had an intercept and slope of 33.1 gm and 0.994. Unlike Shepard's equation, the best equation was not statistically different from the ideal one-to-one relationship between estimated and actual weight. When the new equation was applied to an additional 339 new cases, equally accurate results were obtained. Customizing a laboratory's ultrasonographic weight estimation equations may be necessary to obtain the best estimate of fetal weight.