Does Maternal Body Mass Index Have an Effect on the Accuracy of Ultrasound-Derived Estimated Birth Weight?: A Retrospective Study

Peripartum Prediction of Fetal Weight in Gravidas With Obesity

OBJECTIVES

Estimated fetal weight (EFW) is an important metric at delivery as neonates with abnormal birthweight and their mothers are at higher risk of birth complications. Data regarding optimal EFW assessment in gravidas with obesity is inconsistent, and with the increasing incidence of obesity, clarification of this question is crucial. We aimed to compare accuracy of ultrasound (US)-derived EFW and clinical assessments of EFW in predicting neonatal birthweight among gravidas with obesity.

METHODS

This prospective cohort study enrolled gravidas with obesity and a singleton pregnancy admitted for delivery at term. EFW was determined using either US biometry or clinical assessment (Leopold's maneuvers, Johnson's formula, and Insler's formula) at time of admission. Our primary outcome was accurate EFW, defined as EFW within 500 g of birthweight. Secondary outcomes included ability to predict small-for-gestational age (SGA) and large-for-gestational age (LGA) birthweights. These outcomes were compared between all EFW methods.

RESULTS

A total of 250 gravidas with a median body mass index of 36.4 kg/m2 were enrolled. Admission US outperformed Leopold's maneuvers in obtaining accurate EFW (81.6% versus 74.5%, P = .03). When comparing all methods, Johnson's and Insler's formulae performed the worst, accurately predicting EFW in only 27.4% and 14.3% of cases, respectively. Likewise, US-derived EFW outperformed Leopold's maneuvers and fundal height in the prediction of SGA and LGA neonates.

CONCLUSIONS

US is more accurate than clinical assessment of EFW in gravidas with obesity both for estimation of actual birthweight and prediction of abnormal birthweight. Universal late third-trimester or peripartum US for EFW should be considered in gravidas with obesity.

Accuracy of Estimated Fetal Weight by Ultrasound Versus Leopold Maneuver

ABSTRACT

Estimated fetal weight (EFW) is frequently used for clinical decision-making in obstetrics. The goals of this study were to determine the accuracy of EFW assessments by Leopold and ultrasound and to investigate any associations with maternal characteristics. Postgraduate years 1 and 2 obstetrics and gynecology resident physicians from Harbor-UCLA Medical Center from 2014 to 2020 performed EFW assessments on 10 preterm (<37 weeks' gestational age) fetuses by ultrasound biometry and 10 full-term (≥37 weeks' gestational age) fetuses by ultrasound biometry and Leopold maneuver. Assessments were included if the patients delivered within 2 weeks of the assessments. One thousand six hundred ninety-seven EFW assessments on 1183 patients performed by 33 residents were analyzed; 72.6% of sonographic full-term EFWs, 69% of Leopold full-term EFWs, and 61.5% of sonographic preterm EFWs were within 10% of the neonatal birth weight (BW). The lowest estimation error in our study occurred when actual BW was 3600 to 3700 g. After adjusting for BW, residents were found to have lower accuracy when the mother had a higher body mass index (BMI) for full-term estimation methods (Leopold and ultrasound, β = 0.13 and 0.12, P = 0.001 and 0.002, respectively). Maternal BMI was not related to estimation error for preterm fetuses ( β = 0.01, P = 0.75). Clinical and sonographic EFW assessments performed by obstetrics and gynecology junior residents are within 10% of neonatal BW much of the time. In our cohort, they tended to overestimate EFWs of lower-BW infants and underestimate EFWs of higher-BW infants. Accuracy of full-term EFW assessments seems to decrease with increasing maternal BMI.

Are Junior Residents Accurate at Predicting Fetal Weight? An Analysis of Junior Residents' Performance of Estimated Fetal Weight Using Ultrasound and Leopold's Maneuver

Background

Performing accurate estimated fetal weights (EFWs) is a critical skill developed in obstetrics residency training. Resident physicians are often the first to perform EFWs on obstetric patients when they enter care. Evaluating residents' accuracy in performing EFWs is crucial for assessing their achievement in residency training milestones and providing patient care.

Methods

As part of an educational initiative program between 2014 and 2020, postgraduate year 1 (PGY1) and postgraduate year 2 (PGY2) residents performed EFW measurements on 10 term (>37w0d) patients using ultrasound and Leopold's maneuver and 10 preterm (>24w0d and <37w0d) patients using ultrasound. Clinical characteristics, mode of delivery, and actual birthweights (BWs) were recorded for each patient. The accuracy of these estimates was evaluated using mixed-effect regression models.

Results

Thirty-three residents, 1127 deliveries, and 1790 EFW measurements were evaluated. Overall, the percentage of residents with estimations within 10% of actual BW went up in PGY2 for Leopold's and ultrasound term births, but not for preterm ultrasound births. Maternal body mass index and actual BW were associated with absolute percentage estimation error. After adjusting for these variables, there was a statistically significant decrease in error between PGY1 and PGY2 for Leopold's method in term births; ultrasound (term and preterm) showed more modest reductions in error during PGY2.

Discussion

Resident physicians have accurate estimates of EFWs early in their training, beginning in their first year of residency by both Leopold's maneuver and ultrasound. Furthermore, PGY2 residents performed better than PGY1 residents for Leopold's method.

Accuracy of ultrasound in the estimation of customised birth weight in a public hospital service

INTRODUCTION

Studies have shown that ultrasound estimated foetal weight (EFW) in small for gestational age (SGA) babies tends to be less-accurate when compared to appropriate (AGA) and large (LGA) for gestational age babies. We aimed to analyse the accuracy of ultrasound EFW overall, and by customised birth weight centile category (severe SGA, SGA, AGA, LGA). Also, the accuracy of estimating the centile category using calculated customised EFW centiles.

METHODS

We performed a retrospective study of pregnant women between 20-43 weeks gestation who underwent ultrasound within 7 days of delivery at a large tertiary maternity unit between January 2018 and December 2020. Stillbirths, major foetal anomalies and multiple pregnancies were excluded. The EFW and birth weight were compared, and an accurate estimate defined as ≤15% difference. The customised EFW and birth weight centiles were calculated and used to analyse the accuracy of category prediction.

RESULTS

Of 2061 foetuses included, 92% (n = 1902) were born weighing within 15% of their EFW. Accuracy was not affected by maternal BMI, ethnicity, parity or gestation. 87% of SGA babies were within 15% of their EFW. Ultrasound sensitivity for SGA was 51% (95% CI: 46-55%). The specificity and positive predictive values were 97% (95% CI: 96-98%) and 87% (95% CI: 82-90%) respectively.

CONCLUSION

The accuracy of Ultrasound EFW overall is good, however, is reduced in SGA babies whose EFW and birth weight centile categories tended to be overestimated. The high specificity for SGA supports monitoring with a lowered threshold to intervene in pregnancies identified by ultrasound as SGA.

Percent error of ultrasound examination to estimate fetal weight at term in different categories of birth weight with focus on maternal diabetes and obesity

BACKGROUND

Sonography based estimate of fetal weight is a considerable issue for delivery planning. The study evaluated the influence of diabetes, obesity, excess weight gain, fetal and neonatal anthropometrics on accuracy of estimated fetal weight with respect to the extent of the percent error of estimated fetal weight to birth weight for different categories.

METHODS

Multicenter retrospective analysis from 11,049 term deliveries and fetal ultrasound biometry performed within 14 days to delivery. Estimated fetal weight was calculated by Hadlock IV. Percent error from birth weight was determined for categories in 250 g increments between 2500 g and 4500 g. Estimated fetal weight accuracy was categorized as accurate ≤ 10% of birth weight, under- and overestimated by >  ± 10% - ± 20% and > 20%.

RESULTS

Diabetes was diagnosed in 12.5%, obesity in 12.6% and weight gain exceeding IOM recommendation in 49.1% of the women. The percentage of accurate estimated fetal weight was not significantly different in the presence of maternal diabetes (70.0% vs. 71.8%, p = 0.17), obesity (69.6% vs. 71.9%, p = 0.08) or excess weight gain (71.2% vs. 72%, p = 0.352) but of preexisting diabetes (61.1% vs. 71.7%; p = 0.007) that was associated with the highest macrosomia rate (26.9%). Mean percent error of estimated fetal weight from birth weight was 2.39% ± 9.13%. The extent of percent error varied with birth weight with the lowest numbers for 3000 g-3249 g and increasing with the extent of birth weight variation: 5% ± 11% overestimation in the lowest and 12% ± 8% underestimation in the highest ranges.

CONCLUSION

Diabetes, obesity and excess weight gain are not necessarily confounders of estimated fetal weight accuracy. Percent error of estimated fetal weight is closely related to birth weight with clinically relevant over- and underestimation at both extremes. This work provides detailed data regarding the extent of percent error for different birth weight categories and may therefore improve delivery planning.

Accuracy of ultrasound in estimating fetal weight in New Zealand

Introduction

Ultrasound estimation of fetal weight is an important factor guiding antenatal management. We aimed to review the accuracy of ultrasound in predicting fetal weight and birthweight category and identify influencing factors.

Methods

We performed a retrospective study of term pregnant women who underwent ultrasound within 7 days of delivery at National Women's Health between January 2019 and January 2020. Stillbirths, major fetal anomalies and multiple pregnancies were excluded. Estimated fetal weight (EFW) was calculated using Hadlock formula and compared with birthweights. We evaluated change in weight categories due to these errors.

Results

Of 560 fetuses included, three quarters (n = 425, 76%) of EFWs were within 10% of birthweight. 135 fetuses had EFWs either less than 90% (n = 19) or greater than 110% (n = 116). Fetuses with EFW < 90% had longer times between scanning and delivery, lower EFW and higher maternal BMI. Fetuses with EFW > 110% were associated with higher EFW, later gestational age and older maternal age. US incorrectly estimated 71 (12.7%) fetal birthweight categories. Underestimated weight category (8.9%) was associated with higher maternal BMI.

Discussion

Inaccurate EFWs were more common at the extremes of fetal weight. A significant association was underestimation birthweight in mothers with increased BMI, who are at increased risk for perinatal and surgical complications.

Conclusion

Our accuracy of 76% correctly predicted EFWs compares favourably with previous studies. Clinicians and sonographers should be aware of the increased risk for inaccurate categorisation of fetuses at the extremes of EFW and in mothers with increased BMI.

A routine third trimester growth ultrasound in the obese pregnant woman does not reliably identify fetal growth abnormalities: A retrospective cohort study

BACKGROUND

In response to the challenges of assessing fetal growth in obese women, guidelines recommend routine third trimester ultrasound scans.

AIM

The aim of this study was to assess the diagnostic performance of this routine scan in obese women (body mass index (BMI) ≥ 35 kg/m² ).

METHODS

A retrospective cohort study of 1008 pregnancies with maternal BMI ≥ 35 kg/m² born after 37 weeks gestation at a Victorian hospital from 2015 to 2017. Multiple pregnancies and those affected by diabetes were excluded. Growth ultrasounds were performed between 34 + 0 and 36 + 6 weeks gestation. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for the detection of large for gestational age (LGA > 90%) and small for gestational age (SGA < 10%) were calculated using ultrasound estimated fetal weight (EFW) or abdominal circumference (AC) and compared with gestational age and gender-based birthweight percentiles.

RESULTS

Using EFW, sensitivity for detecting SGA at birth was 8.1% (six of 74) with a PPV of 100%. Sensitivity for detecting LGA at birth was 61.0% (119 of 195), PPV 54.8%. Sensitivity, specificity, PPV and NPV percentages were all lower using AC. Only 40% of actual birthweight percentiles (405/1008) were within ±10 percentiles of their growth ultrasound EFW percentile.

CONCLUSION

The performance of a routine third trimester ultrasound in women with BMI ≥ 35 kg/m² suggests limited utility in helping identify aberrant fetal growth. This has important implications for the management of obese pregnant women.

Associations between estimated foetal weight discordance and clinical characteristics within dichorionic twins: The NICHD Fetal Growth Studies

BACKGROUND

Birthweight discordance is well studied, with less known about longitudinal inter-twin differences in foetal growth.

OBJECTIVE

To examine inter-twin per cent differences in EFW (EFW_% ), head (HC_% ) and abdominal circumference (AC_% ), and femur length (FL_% ) across gestation in dichorionic twin gestations and explore associated characteristics.

METHODS

Foetal biometrics were assessed by ultrasound and EFW calculated at ≤6 study visits among women with dichorionic twin pregnancies enrolled in the NICHD Fetal Growth Studies cohort (US, 2012-2013). Inter-twin per cent difference was defined: ([Size_{larger twin}  - Size_{smaller twin} ]/Size_{larger twin}  × 100). Linear mixed models evaluated per cent differences in foetal biometrics at 15 weeks and their change per week overall and by maternal/neonatal characteristics in unadjusted and adjusted models.

RESULTS

In 140 pregnancies, inter-twin per cent differences increased across gestation for EFW (0.18%/week, 95% confidence interval [CI] 0.10, 0.27), HC (0.03%/week, 95% CI 0.00, 0.06), and AC (0.03%/week, 95%CI -0.01, 0.08) but decreased for FL (-0.03%/week, 95% CI -0.09, 0.02). After adjustment, change in EFW_% difference across gestation differed by pre-pregnancy body mass index (BMI [kg/m² ]; underweight [<18.5]; normal weight [18.5-24.9]; overweight [25.0-29.9]; obese [≥30.0]; P_interaction  = .022); and conception method (in vitro fertilisation [IVF], intrauterine insemination, ovulation induction medication, donor egg/embryo, none; P_interaction  = .060). While EFW_% difference increased with normal pre-pregnancy BMI (0.24%/week, 95% CI 0.12, 0.37), little change was noted with pre-pregnancy obesity (0.01%/week, 95% CI -0.15, 0.17). EFW_% difference increased in conceptions without fertility treatments (0.23%/week, 95% CI 0.11, 0.34) but not IVF conceptions (-0.00%/week, 95% CI -0.16, 0.16). Similar patterns of differences across gestation were noted for HC_% by conception method (P_interaction  = .026) and AC_% by pre-pregnancy BMI (P_interaction  = .071); changes in HC_% differed by parity (nulliparous, multiparous; P_interaction  = .004).

CONCLUSIONS

EFW_% difference increased across gestation in dichorionic twins, but remained stable with pre-pregnancy obesity or IVF conception, patterns mirrored for HC and AC. Research is needed to understand pathologic versus physiologic differential twin growth trajectories.

Can we improve the gestation-adjusted projection (GAP) method for prediction of birth weight in morbidly obese women?. J Matern Fetal Neonatal Med 2018;32:3600-3605. [PMID: 29681190 DOI: 10.1080/14767058.2018.1468882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Objective: The gestation-adjusted projection (GAP) is a method to predict birthweight using population birth data and third trimester ultrasound fetal weight. This method usually utilizes population birth weight data from almost 40 years ago. In 2011, a large cohort of racially diverse infants across the US was included to validate updated birth curves. Our objective was to determine if the updated data would improve the accuracy of the GAP method during the third trimester among obese women. Methods: This secondary analysis of a cohort study included singleton pregnancies of obese women who had fetal growth assessment(s) in the third trimester. The first subgroup (N = 235) included women with a BMI >40 kg/m² who had ultrasounds during 30 + 0-35 + 0 weeks (EARLY) and greater than 35 + 0 weeks (LATE). The second subgroup (N = 431) included women with a BMI 30-35, 40-50, or >50 kg/m² who had an ultrasound during 34 + 0-36 + 6 weeks. Mean absolute percent error was calculated for all GAP methods and compared using paired t-tests. Sensitivity, specificity, and area under the curve for diagnosis of birth weight >4000 grams were also estimated for each GAP method. Results: The mean absolute percent error for the first subgroup (N = 235) using historical population birth weights was 7.4-7.9%. After using updated population birth weight curves using all neonates, the mean absolute percent error for the first subgroup ranged between 7.6 and 9.4%. GAP predictions using all neonates, as well as male and female-specific birth data compared to the historical population data during both the EARLY and LATE periods were significantly worse (p < .01). The mean absolute percent error for the second subgroup (N = 431) using historical population birth weights ranged from 7.2 to 7.9%. The absolute percent error using gender-specific compared to historical data was significant in the BMI 30-35 group (male 8.1% versus historical 7.6%, p < .01, female 8.1% versus historical 7.6%, p < .01). The differences in absolute percent error between historical and updated population data became less evident in the BMI 40-50 and >50-kg/m² groups (p = .05 and p = .15, respectively) though still overall performed worse with the updated data. Conclusions: Prediction of birth weight using the GAP method does not seem to be improved among obese women after using updated population data. Alternatively, modeling techniques may need to be applied to improve the accuracy of the GAP method.