Influence of Maternal Body Mass Index on the Clinical Estimation of Fetal Weight in Term Pregnancies

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.

Investigating the accuracy of Johnson's rule in estimating fetal weight

BACKGROUND

Birth weight has a significant impact on perinatal mortality. Therefore, the estimation of fetal weight greatly influences the policies necessary for care during and after delivery. We aimed to investigate Johnson's rule in estimating fetal weight.

MATERIALS AND METHOD

This study was a single-group longitudinal study that was conducted in 6 months from October 2021 to April 2022 on 150 pregnant women in Isfahan-Iran. The sampling method was accessible. Inclusion criteria include being term, singleton, without abnormality, intact membranes, cephalic presentation, and exclusion criteria include diagnosed polyhydramnios or oligohydramnios and mother's abdominal or pelvic known masses. After completing the informed consent, fetal weight was estimated by Johnson's rule and was compared with the birth weight. Descriptive and analytical statistics (mean-standard deviation (SD), number-percentage, t-paired, and Spearman's correlation coefficient) were used to achieve the objectives of the study. The receiver operating characteristic (ROC) curve was also used to determine the sensitivity, specificity, and positive and negative predictive value of Johnson's law.

RESULT

The mean (SD) birth weight was 3032.88 ± 481.11 g and the mean (SD) estimated fetal weight (EFW) by the clinical method was 3152.15 ± 391.95 g. There was a significant difference between the averages (P < 0.001). The percentage error of EFW showed a significant negative correlation (r = -0.286; P < 0.05) with gestational age (GA) and a significant positive correlation (r = 0.263; P < 0.05) with the fetal head station. The sensitivity and specificity of EFW with Johnson's rule, in normal fetal birth weight, were higher than in low birth weight fetal. The accuracy of EFW with ± 10% of the actual weight was higher in average for gestational age (AGA) (84.3%) and high-for-gestational-age (LGA) (70%) than in low-for-gestational-age (SGA) (4%). The EFW mean percentage error in SGA was higher than in the other two weight groups. This method, especially for AGA and LGA fetuses, can be a suitable alternative to other weight estimation methods.

CONCLUSION

Clinical estimation of weight via Johnson's rule due to availability and no cost can be a suitable method for managing childbirth based on fetal weight.

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.

Accuracy of Fetal Weight Estimation by Ultrasonographic Evaluation in a Northeastern Region of India

Methods

The cross-sectional study included 100 pregnant women aged 20–45 years from the Kamrup district admitted to Guwahati Medical College and Hospital, Guwahati, Assam. The data were analyzed using Microsoft Excel and SPSS version 16. The EFW at term was calculated using Shepard's formula and Hadlock's formula. Differences in means are compared using the one-way ANOVA or Kruskal–Wallis test and paired t-test. The accuracy of the two procedures was evaluated using mean absolute error (MAE) and mean absolute percentage error (MAPE). A p value<0.05 was considered significant.

Results

The present study included 100 pregnant women aged 21–38 years with term or postterm pregnancies subjected to ultrasonographic evaluation within 72 hours of delivery. The mean (±s.d.) EFW by Shepard's formula was 2716.05 (±332.38) g and Hadlock's formula was 2740.44 (±353.23) g, respectively. For Hadlock's formula, MAE ± s.d. was found to be higher (overall 84.59 ± 76.54) specifically in the weight category less than 2500 (106.42 ± 88.11) as compared to Shepard's (overall MAE ± s.d = 79.86 ± 64.78, and among ABW < 2500 g, MAE ± s.d = 65.04 ± 61.02). The overall MAPE of Hadlock's formula was 3.14% and that for Shepard's formula was 2.91%, and the difference was not statistically significant. Both Shepard's formula and Hadlock's formula had a sensitivity of 92.85% in detecting IUGR, but Hadlock's method had higher specificity (66%), higher PPV (86.67%), and higher NPV (80%).

Conclusion

The ultrasonographic evaluation of fetal weight helps predict fetal birth weight precisely and can influence obstetric management decisions concerning timing and route of delivery, thus reducing perinatal morbidity and mortality.

Influence of maternal body mass index on interobserver variability of fetal ultrasound biometry and amniotic-fluid assessment in late pregnancy

OBJECTIVE

To determine the interobserver reproducibility of fetal ultrasound biometric and amniotic-fluid measurements in the third trimester of pregnancy, according to maternal body mass index (BMI) category.

METHODS

This was a prospective cohort study of women with a singleton gestation beyond 34 weeks, recruited into four groups according to BMI category: normal (18.0-24.9 kg/m² ), overweight (25.0-29.9 kg/m²⁾ , obese (30.0-39.9 kg/m² ) and morbidly obese (≥ 40 kg/m² ). Multiple pregnancies, women with diabetes and pregnancies with a fetal growth, structural or genetic abnormality were excluded. In each woman, fetal biometric (biparietal diameter (BPD), head circumference, abdominal circumference (AC), femur length (FL) and estimated fetal weight) and amniotic-fluid (amniotic-fluid index (AFI) and maximum vertical pocket (MVP)) measurements were obtained by two experienced sonographers or physicians, blinded to gestational age and each other's measurements. Differences in measurements between observers were expressed as gestational age-specific Z-scores. The interobserver intraclass correlation coefficient (ICC) and Cronbach's reliability coefficient (CRC) were calculated. Bland-Altman analysis was used to assess the degree of reproducibility.

RESULTS

In total, 110 women were enrolled prospectively (including 1320 measurements obtained by 17 sonographers or physicians). Twenty (18.2%) women had normal BMI, 30 (27.3%) women were overweight, 30 (27.3%) women were obese and 30 (27.3%) women were morbidly obese. Except for AFI (ICC, 0.65; CRC, 0.78) and MVP (ICC, 0.49; CRC, 0.66), all parameters had a very high level of interobserver reproducibility (ICC, 0.72-0.87; CRC, 0.84-0.93). When assessing reproducibility according to BMI category, BPD measurements had a very high level of reproducibility (ICC ≥ 0.85; CRC > 0.90) in all groups. The reproducibility of AC and FL measurements increased with increasing BMI, while the reproducibility of MVP measurements decreased. Among the biometric parameters, the difference between the BMI categories in measurement-difference Z-score was significant only for FL. Interobserver differences for biometric measurements fell within the 95% limits of agreement.

CONCLUSION

Obesity does not seem to impact negatively on the reproducibility of ultrasound measurements of fetal biometric parameters when undertaken by experienced sonographers or physicians who commonly assess overweight, obese and morbidly obese women. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

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.

Identification of newborns with birthweight ≥ 4,500g: Ultrasound within one- vs. two weeks of delivery

OBJECTIVE

Our objective was to compare the diagnostic characteristics of sonographic estimated fetal weight (SEFW) done within 7 versus 8-14 days before delivery for detection of fetal macrosomia (birthweight ≥ 4500 g).

STUDY DESIGN

We performed a multicenter, retrospective cohort study of all non-anomalous singletons with SEFW ≥ 4000 g by Registered Diagnostic Medical Sonographers conducted within 14 days of delivery. Cohorts were grouped by time interval between ultrasound and delivery: 0-7 days versus 8-14 days. The detection rate (DR) and false positive rate (FPR) for detection of birthweight (BW) ≥ 4500 g were compared between groups with subgroup analysis for diabetic women. Area under the receiver operator curve (AUC) was calculated to analyze all possible SEFW cutoffs within our cohort.

RESULTS

A total of 330 patients met inclusion criteria with 250 (75.8 %) having SEFW within 7 days and 80 (24.2 %) with SEFW 8-14 days prior to delivery. The rate of macrosomia was 15.1 % (N = 51). The DR for macrosomia was significantly higher when SEFW was performed within 7 days of delivery compared to 8-14 days among non-diabetic (73.0 % vs 7.1 %; p < 0.001) and diabetic women (76.5 % vs 16.7 %; p = 0.02). There was no significant change in FPR in either group. The AUC for detection of macrosomia was significantly higher when SEFW was performed within 7 days versus 8-14 days (0.89 vs 0.63; p < 0.01).

CONCLUSION

With SEFW ≥ 4000 g, the detection of BW ≥ 4500 g is significantly higher when the sonographic examination is within 7 days of birth irrespective of maternal diabetes.

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.

Identifying fetal growth disorders using ultrasound in obese nulliparous women

OBJECTIVE

We evaluated the ability of third trimester ultrasound to diagnose fetal growth disorders among obese women.

METHODS

This is a retrospective cohort study of obese nulliparous women who delivered term singleton neonates who had an ultrasound within 5 weeks of delivery. We characterized the sensitivity, specificity, positive predictive value and negative predictive value of ultrasound to detect large-for-gestational age (LGA) and small-for-gestational age (SGA) infants. Antenatally, LGA and SGA were defined as an ultrasound estimated fetal weight >90% or <10% based on the Hadlock formula. Postnatally, LGA or SGA designation was based on gestational age-based birthweight percentiles. Test characteristics were analyzed for the total cohort and by class of obesity (class II, body mass index [BMI] = 35.0-39.9 kg/m² versus class III, BMI ≥ 40 kg/m²). We compared the area under the curve for receiver-operating characteristic (ROC) curves for different classes of obesity.

RESULTS

Of 690 women, 13 (1.9%) screened positive for SGA and 19 (2.8%) delivered an SGA neonate. In contrast, 158 (22.9%) screened positive for LGA and 97 (14.1%) delivered an LGA neonate. The sensitivity of ultrasound for SGA was 26.3% and the specificity was 98.8%. The sensitivity for LGA was 75.3% and the specificity was 85.7%. The ROC curves did not differ significantly for different classes of obesity (p = .69 for SGA, p = .75 for LGA).

CONCLUSION

Ultrasound in obese women who delivered term pregnancies has a high specificity but poor sensitivity for SGA and a low positive predictive value for LGA.

Fetal weight estimation at term - ultrasound versus clinical examination with Leopold's manoeuvres: a prospective blinded observational study

BACKGROUND

Fetal weight estimation is of key importance in the decision-making process for obstetric planning and management. The literature is inconsistent on the accuracy of measurements with either ultrasound or clinical examination, known as Leopold's manoeuvres, shortly before term. Maternal BMI is a confounding factor because it is associated with both the fetal weight and the accuracy of fetal weight estimation. The aim of our study was to compare the accuracy of fetal weight estimation performed with ultrasound and with clinical examination with respect to BMI.

METHODS

In this prospective blinded observational study we investigated the accuracy of clinical examination as compared to ultrasound measurement in fetal weight estimation, taking the actual birth weight as the gold standard. In a cohort of all consecutive patients who presented in our department from January 2016 to May 2017 to register for delivery at ≥37 weeks, examination was done by ultrasound and Leopold's manoeuvres to estimate fetal weight. All examiners (midwives and physicians) had about the same level of professional experience. The primary aim was to compare overall absolute error, overall absolute percent error, absolute percent error > 10% and absolute percent error > 20% for weight estimation by ultrasound and by means of Leopold's manoeuvres versus the actual birth weight as the given gold standard, namely separately for normal weight and for overweight pregnant women.

RESULTS

Five hundred forty-three patients were included in the data analysis. The accuracy of fetal weight estimation was significantly better with ultrasound than with Leopold's manoeuvres in all absolute error calculations made in overweight pregnant women. For all error calculations performed in normal weight pregnant women, no statistically significant difference was seen in the accuracy of fetal weight estimation between ultrasound and Leopold's manoeuvres.

CONCLUSIONS

Data from our prospective blinded observational study show a significantly better accuracy of ultrasound for fetal weight estimation in overweight pregnant women only as compared to Leopold's manoeuvres with a significant difference in absolute error. We did not observe significantly better accuracy of ultrasound as compared to Leopold's manoeuvres in normal weight women. Further research is needed to analyse the situation in normal weight women.

Influence of maternal obesity on the accuracy of ultrasonography birth weight prediction

Objective: The aim of the study was to investigate whether the accuracy of ultrasound estimates of fetal weight (EFW) was dependent on maternal obesity.Study design: A prospective cross-sectional study of 1064 singleton pregnant women classified according to body mass index (BMI) into two categories: normal (BMI < 25 kg/m², n = 863) and obese (BMI ≥ 35 kg/m², n = 201) was conducted. EFW were calculated using Hadlock's formula, and the difference between EFW and the actual birthweight (absolute percent error) was analyzed in both groups. Spearman's correlation was used to assess the relationship between ultrasound performance (absolute error), maternal BMI, and actual birth weight.Results: Median absolute error of sonographic EFW was 5.90 and 6.47% for the normal and obese groups, respectively (p .38). A correlation between EFW and birth weight (BW) was found in both groups, r = 0.755 (p < .001) and r = 0.753 (p < .001), respectively. The correlation between absolute error, maternal BMI, and fetal birth weight was poor.Conclusions: Maternal obesity is unrelated to the accuracy of sonographic EFW, and regardless of maternal or fetal size, ultrasound is currently an accurate method of prediction for both obese and normal weight pregnant women.

Accuracy of sonographic fetal weight estimation in full-term singleton pregnant women

OBJECTIVES

To investigate the factors which might influence the sonographic fetal weight estimation (SFWE) accuracy.

METHODS

This prospective study was conducted among 949 singleton term pregnant women who delivered at a tertiary center, from January 2017 to December 2017. All participants' maternal (i.e. parity, age, body mass index and gestational weight gain during pregnancy), fetal sonographic (i.e. fetal presentation, amniotic fluid index, localization of placenta and estimated fetal weight) and neonatal (birth weight and gender) characteristics were recorded. A p<0.05 was considered significant.

RESULTS

The mean absolute percent error (APE) values of SFWE was 8.2±6.5 percent, and overall failure ratio (APE >10%) was 33%. In failure group, primiparous woman and cephalic presentation fetus were significantly more common compared to accuracy group (55.9% vs.44.8%; p=0.001 and 98% vs. 95.2%; p=0.03, respectively). In contrast, the mean neonatal birth weight (NBW) value was significantly lower in failure group compared to success group (3250±565 gr vs. 3404±410 gr; p=0.001). The correlation between SFWE and NBW was linear, however negative, and significant (p=0.001). Logistic regression analysis revealed that primiparous woman, cephalic presentation fetus and <3300 gr NBW were independent risk factors for the SFWE failure (relative risks were 1.6, 2.8 and 2.4 respectively, p<0.05).

CONCLUSION

SFWE has a high correlation with NBW, however it's accuracy is still unsatisfactory, and depend on many unpredictable and inconsistent factors.

Maternal Body Mass Index and Amniotic Fluid Index in Late Gestation

OBJECTIVES

To determine the effect, if any, of an increasing maternal body mass index (BMI) on sonographically diagnosed oligohydramnios in late gestation and how it subsequently affects obstetric and neonatal outcomes.

METHODS

This retrospective cohort study evaluated all women with singleton gestations who had a sonographic examination at 40 to 42 weeks' gestational age at North Shore University Hospital from 2010 through 2013. Underweight women (prepregnancy BMI < 18.5 kg/m² ) were excluded because of higher rates of oligohydramnios and fetal growth restriction. Patients were classified into 5 groups by late-pregnancy BMI. The primary variable of interest was the diagnosis of oligohydramnios (amniotic fluid index < 5 cm). Secondary variables of interest included the mode of delivery and indication for primary cesarean delivery. A multivariable logistic regression analysis was performed.

RESULTS

Oligohydramnios was identified in 189 of 1671 patients (11.3%). There was no significant difference in the amniotic fluid index between BMI groups. The rate of primary cesarean delivery increased with each successive BMI group (P < .001) such that women in the class III obesity group had an approximately 3-fold higher rate of primary cesarean delivery than women in the normal BMI group and a 2-fold higher rate than women in the overweight BMI group. In the final multivariable logistic regression model, a high BMI, nulliparity, and excessive gestational weight gain were associated with primary cesarean delivery. However, oligohydramnios did not contribute significantly to the model.

CONCLUSIONS

The maternal BMI is not associated with oligohydramnios in late gestation. An increasing maternal BMI significantly increases the risk of primary cesarean delivery.

Attempted and Successful Vacuum-Assisted Vaginal Delivery by Prepregnancy Body Mass Index

OBJECTIVE

To examine rates of attempted and successful vacuum-assisted vaginal delivery by prepregnancy body mass index (BMI).

METHODS

We conducted a retrospective cohort study of 2,084 women with singleton gestations needing operative delivery assistance and vacuum-eligible (fully dilated, +2 station or greater, 34 weeks of gestation or greater) using 2006-2014 inpatient records. Prepregnancy BMI was categorized as underweight (less than 18.5), normal weight (18.5 to less than 25), overweight (25 to less than 30), or obese (30 or greater). Logistic regression models estimated odds ratios (ORs) and 95% confidence intervals (CIs) of attempted and successful vacuum-assisted vaginal delivery by prepregnancy BMI adjusted for age, race, marital status, parity, diabetes, labor induction-augmentation, episiotomy, gestational age, and neonatal birth weight.

RESULTS

Thirty-nine percent of women requiring delivery assistance and eligible for a vacuum were overweight or obese, 79% had vacuum attempts, and 95.3% of attempted vacuum-assisted vaginal deliveries were successful. Compared with women who were normal weight prepregnancy (82.8%), women who were overweight or obese were less likely to have vacuum attempted (75.8%, OR 0.71, 95% CI 0.53-0.96 and 71.2%, OR 0.53, 95% CI 0.39-0.74, respectively). Among women with attempted vacuum-assisted vaginal delivery, successful delivery did not differ by prepregnancy BMI (92.6%, OR 0.54, 95% CI 0.21-1.37 for underweight; 94.5%, OR 1.07, 95% CI 0.57-2.00 for overweight; 96.3%, OR 1.09, 95% CI 0.51-2.33 for obese compared with 95.6% among normal-weight women).

CONCLUSION

Among women in need of operative delivery assistance, prepregnancy obesity was associated with lower likelihood of attempted vacuum-assisted vaginal delivery but, if attempted, success rates were similar to rates among normal-weight women. With significant morbidity of second-stage cesarean delivery in obese women, research should examine whether vacuum-assisted vaginal delivery may be appropriate for additional obese patients.

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

OBJECTIVES

The purpose of this study was to investigate the relationship between the maternal body mass index (BMI) and the accuracy of ultrasound-derived birth weight.

METHODS

A retrospective chart review was performed on women who had an ultrasound examination between 36 and 43 weeks' gestation and had complete delivery data available through electronic medical records. The ultrasound-derived fetal weight was adjusted by 30 g per day of gestation that elapsed between the ultrasound examination and delivery to arrive at the predicted birth weight.

RESULTS

A total of 403 pregnant women met inclusion criteria. Age ranged from 13-44 years (mean ± SD, 28.38 ± 5.97 years). The mean BMI was 32.62 ± 8.59 kg/m² . Most of the women did not have diabetes (n = 300 [74.0%]). The sample was primarily white (n = 165 [40.9%]) and Hispanic (n = 147 [36.5%]). The predicted weight of neonates at delivery (3677.07 ± 540.51 g) was higher than the actual birth weight (3335.92 ± 585.46 g). Based on regression analyses, as the BMI increased, so did the predicted weight (P < .01) and weight at delivery (P < .01). The accuracy of the estimated ultrasound-derived birth weight was not predicted by the maternal BMI (P = .22). Maternal race and diabetes status were not associated with the accuracy of ultrasound in predicting birth weight.

CONCLUSIONS

Both predicted and actual birth weight increased as the BMI increased. However, the BMI did not affect the accuracy of the estimated ultrasound-derived birth weight. Maternal race and diabetes status did not influence the accuracy of the ultrasound-derived predicted birth weight.

Ultrasound versus Clinical Examination to Estimate Fetal Weight at Term

Introduction At term, fetal weight estimation is an important factor for decisions about the delivery mode and the timing of labor induction. This study aimed to compare the accuracy of abdominal palpation with that of ultrasound performed by different examiners to estimate fetal weight. The study investigated whether differences in the examiners' training affected fetal weight estimates. The accuracy of the weight estimates made for fetuses with extreme birth weights was also evaluated. Finally, the accuracy of Johnson's method and of Insler and Bernstein's formula for estimating fetal weight were compared with the other two methods. Methods This prospective study included singleton pregnancies between 37 weeks of gestation and 12 days post-term planned for vaginal delivery or cesarean section. Ultrasound and abdominal palpation using Leopold's maneuvers were performed by examiners with different levels of professional experience. Fetal weight was additionally estimated using Insler and Bernstein's formula and Johnson's method. Statistical analysis calculated the accuracy of fetal weight estimates for the different examiners and the four methods. Results A total of 204 women were included in the analysis. Trained ultrasound examiners were most accurate when estimating fetal weight compared with all other examiners. The comparison of all four methods showed that fetal weight was assessed most accurately with ultrasound. No learning curve could be established. BMI and advanced gestational age affected the accuracy of the estimated weight. The analysis showed that a greater deviation between estimated weight and actual weight occurred with all four methods for fetuses at either end of the extremes of fetal weight, i.e., with very low or very high birth weights. Conclusion Fetal weight should be estimated using ultrasound. A good ultrasound training is essential.

Accuracy of Sonographically Estimated Fetal Weight Near Delivery in Pregnancies Complicated With Diabetes Mellitus

OBJECTIVES

The purpose of this study was to evaluate the accuracy of sonographic estimations of fetal weight (FW) and signed percent error between pregnant patients with and without diabetes mellitus (DM).

METHODS

We conducted a retrospective cohort study of all singleton nonanomalous live births who delivered after 34 weeks and received a sonographic estimation of FW within 2 weeks of delivery at the University of Cincinnati Medical Center between 2008 and 2011. Our primary outcome compared the ΔFW and signed percent error between DM and non-DM pregnancies. Sensitivity and specificity were calculated for the prediction of FW greater than 4000 g in each study group. Linear regression analysis assessed correlation coefficients, R² values, and variance of the ΔFW by live birth weight.

RESULTS

The mean ΔFWs were 62 and 103 g for non-DM and DM pregnancies, respectively (P = .04). However, the signed percent error (mean ± SD, 1.7% ± 9.8% versus 2.6% ± 9.9%; P = .15) was similar between the study groups. Linear regression comparing the ΔFW to the live birth weight revealed a weak correlation in DM (r = 0.34; R²  = 0.11) and non-DM pregnancies, (r = 0.17; R²  = 0.03) pregnancies. Overall sensitivity for the prediction of FW greater than 4000 g was poor (0.41 and 0.62 in non-DM and DM pregnancies). However, the specificity was high (0.97 and 0.99 for both groups).

CONCLUSIONS

Although DM alters the biometric measurements of the fetus with increasing thoracoabdominal size, there are no clinically significant alterations in the accuracy of sonography for FW prediction when performed near delivery. Sonography is highly specific for birth weight greater than 4000 g, which is helpful for delivery planning and management.

Accuracy of clinical fetal weight estimation by Midwives

BACKGROUND

Clinical fetal weight estimation is a common practice in obstetrics. This study aims to evaluate the accuracy of fetal weight estimation by midwives, and to identify factors that may lead to overestimation or underestimation of fetal weight.

METHODS

A cohort prospective study in a Lebanese university hospital, included weight estimation of singleton pregnancies above 35 weeks. Multiple pregnancies, unclear dating, growth retardation, malformations and stillbirths cases are excluded. The estimated fetal weight is recorded by midwives in a sealed envelope and compared to true weight later. The effects of BMI, weight gain, parity, diabetes, hypertension, neonate's sex and weight, uterine contractions, rupture of membranes and daytime or nighttime shift on these estimations were assessed.

RESULTS

One hundred and sixty-six patients were included. Mean birth weight was 3246 ± 362 g. Mean absolute percentage error of weight estimation was 8.5 ± 6.7% (0-30.9%). Estimation was within the correct range of ±10% in 63% of cases. Maternal and fetal factors did not significantly change weight estimation. Fetuses with birth weights more than 4000 tended to be underestimated by midwives. Estimation improved over time (nonsignificant).

CONCLUSIONS

Maternal and fetal factors, except for macrosomia, have limited impact on estimation of fetal birth weight. Macrosomia is challenging because of a consistent tendency of underestimation by midwives.

Comparison of 2- and 3-Dimensional Sonography for Estimation of Birth Weight and Neonatal Adiposity in the Setting of Suspected Fetal Macrosomia

OBJECTIVES

To compare the accuracy of 2-dimensional (2D) and 3-dimensional (3D) fetal measurements for prediction of birth weight Z score and neonatal adiposity (percent body fat) in the setting of suspected fetal macrosomia.

METHODS

We conducted a prospective observational study of term singleton pregnancies with suspected macrosomia. Patients were enrolled on admission to labor and delivery and underwent sonographic examinations. Within 48 hours of delivery, neonatal anthropometric measurements were obtained.

RESULTS

Thirty-four neonates were included in the analysis. Mothers were very obese (mean body mass index ± SD, 39.1 ± 7.8 kg/m(2)); 56.5% were white; and 39.1% had diabetes. Neonates were 38% female and had a mean birth weight of 3940.0 ± 496.8 g, percent body fat of 18.5% ± 4.0%, and Ponderal index of 2.8 ± 0.3 g/cm(3). Mean 2D estimated fetal weight was 3973 ± 443 g; mean 3D estimated fetal weight was 3803 ± 528 g; and mean thigh volume was 102.5 ± 19.6 cm(3). Both 2D and 3D measurements accounted for about half the variance in predicted birth weight (R(2) for 2D = 0.53, 71% within 10% of birth weight; R(2) for 3D = 0.47, 65% within 10% of birth weight). Thigh volume Z score was the prenatal parameter most highly correlated with both birth weight Z score (R(2) = 0.52; r = 0.72; 95% confidence interval, 0.54-0.84; P < .001) and percent body fat (R(2) = 0.22; r = 0.47; 95% confidence interval, 0.17-0.69; P = .04).

CONCLUSIONS

In our population of fetuses with suspected macrosomia, fractional thigh volume was the best sonographic estimate of neonatal percent body fat and birth weight Z score. Future research on prediction of neonatal weight and adiposity in macrosomic fetuses should include an estimate of fetal soft tissue given the generalized increase in body fat of these fetuses.

The Suspected Macrosomic Fetus at Term: A Clinical Dilemma

Estimation of fetal weight is an important component of antenatal and intrapartum management of pregnant women. While many clinicians use ultrasound estimates of fetal weight to assess fetal growth, there are inherent challenges in both the diagnosis and management of suspected fetal macrosomia. Given the inaccuracy in estimating fetal weight, and the risks that accompany cesarean birth or induction of labor, the management of suspected fetal macrosomia requires open communication and shared decision making between the woman and her health care providers. This case study and literature review highlight the current management and recommendations for suspected fetal macrosomia.

Analysis of the effectiveness of ultrasound and clinical examination methods in fetal weight estimation for term pregnancies

Objective:

To compare the accuracy of clinical and ultrasonographic (USG) estimation of fetal weight in non-complicated, term pregnancies.

Materials and Methods:

Two hundred term pregnant women were included in the study. We used three formulae for the estimation of fetal weight at term; the Hadlock formula for the USG method, and two different formulas for clinical methods, maternal symphysis-fundal height and abdominal circumference at the level of umbilicus. Accuracy was determined by mean percentage error, mean absolute percentage error and proportion of estimates within 10% of actual birth weight (birth weight ±10%). Patients were divided into two groups according to actual birth weight, the normal birth weight group (2500-3999 g) and high birth weight group (≥4000 g).

Results:

All three methods statistically overestimated birth weight for the high and normal birth weight groups (p<0.001, p=1.000, p=0.233) (p=0.037, p<0.001, and p<0.001). For both groups, the mean absolute percentage errors of USG were smaller than for the other two clinical methods and the number of estimates were within 10% of actual birth weight for USG was greater than for the clinical methods; the differences were statistically significant (p<0.001). No statistically significant difference of accuracy was observed for all three methods for the high birth weight group (p=0.365, p=0.768, and p=0.540). However, USG systematically underestimated birth weight in this group.

Conclusion:

For estimation of fetal birth weight in term pregnancies, ultrasonography is better than clinical methods. In the suspicion of macrosomia, it must be remembered that no method is better than any other. In addition, if ultrasonography is used, careful management is recommended because ultrasonography overestimates in this group.

Sonographic fetal weight estimation in normal and overweight/obese healthy term pregnant women by gestation-adjusted projection (GAP) method

PURPOSE

The objective of this study is to assess the ultrasound accuracy in fetal weight estimation related to the time distance between the actual weight recorded at delivery and the period of sonography among normal and overweight/obese pregnant women within 3 weeks prior birth at term.

METHODS

Four-hundred and ninety patients with healthy pregnancy were studied in a cohort study. The absolute percent error in estimation was achieved by gestation-adjusted projection method from Hadlock model for weight calculation as measure of accuracy. The mean percentage error variation over the weeks was correlated to maternal body mass index (BMI, Kg/m(2)) at ultrasound. The relationship between BMI and ultrasound performance was assessed by linear regression.

RESULTS

The overall proportion of supposed sonographic estimated fetal weight at birth within ±10 % of the birth weight significantly declines over the weeks (P = .016). The trend toward a progressive deterioration in ultrasound accuracy is not statistically significant for normal weight women (P = .272) but it is for over-weight/obese (P = .044). On univariate analysis, the absolute percent error and absolute error are positively related to BMI.

CONCLUSIONS

Accuracy is related to the week at ultrasound scan with a gradual deterioration over the time and it worsens with increasing distance in days between the date of ultrasounds and delivery. The deterioration is greater for BMI ≥ 25.

The utility of ultrasound surveillance of fluid and growth in obese women

OBJECTIVE

The purpose of this study was to evaluate the utility of ultrasound surveillance in obese women.

STUDY DESIGN

This is a retrospective cohort of all obese women who underwent sonography at a single center from 2005-2013. Inclusion criteria were body mass index ≥30 kg/m(2), singleton, ≥1 ultrasound scan performed at <20 weeks of gestation, and ≥1 ultrasound scan performed at ≥24 weeks of gestation. Pregnancies with medical complications, fetal anomalies, or preterm premature rupture of membranes were excluded. Outcomes that were considered were small for gestational age, large for gestational age (LGA), macrosomia, oligohydramnios, and polyhydramnios. We calculated the number needed to screen (NNS) and 95% confidence interval (CI) for scans that were performed during 3 gestational age ranges (24-31 weeks 6 days, 32-35 weeks 6 days, and ≥36 weeks).

RESULTS

Two thousand two sonograms were performed in 1164 obese women at ≥24 weeks of gestation. Small for gestational age was diagnosed in 59 pregnancies (5.1%); 7 pregnancies (0.6%) were diagnosed at <32 weeks of gestation (NNS, 159; 95% CI, 69-490). LGA was diagnosed in 38 cases (3.3%); only 1 case was identified at <32 weeks of gestation and was not LGA at birth. For every 29 (95% CI, 19-46) scans performed at >36 weeks of gestation, 1 case of macrosomia was identified. Amniotic fluid abnormalities were diagnosed in 44 pregnancies (3.8%; oligohydramnios, 19; polyhydramnios, 25); 34.1% abnormalities were diagnosed at <32 weeks of gestation (NNS: oligohydramnios, 113; 95% CI, 55-282 for oligohydramnios; polyhydramnios, 100; 95% CI, 50-230). At ≥36 weeks of gestation, 7 (95% CI, 6-8) scans were needed to diagnose any fluid or growth abnormality.

CONCLUSION

In obese women without comorbidities, few sonographic diagnoses of amniotic fluid or fetal growth abnormalities are made at <32 weeks of gestation. Therefore, if a policy of serial sonographic surveillance is used, we suggest ultrasound scans for fluid and growth in obese women to begin at ≥32 weeks of gestation.

Clinical accuracy of estimated fetal weight in term pregnancies in a teaching hospital

OBJECTIVE

To evaluate whether clinical characteristics alter the accuracy of clinical estimation of fetal weight (EFW) in term pregnancies in a teaching hospital.

METHODS

Secondary analysis of a retrospective cohort study of patients presenting for labor at term. Clinical EFW was performed using Leopold maneuvers. A Spearman's rank correlation coefficient (r) was used to evaluate the linear relationship between clinical EFW and actual birth weight (BW). Body mass index (BMI), gestational age, fetal station, and admission diagnosis were evaluated with respect to their impact on clinical EFW. The primary outcome was an absolute error between clinical EFW and actual BW >500 g.

RESULTS

Of 3797 patients, 941 (24.8%) had an absolute error in clinical EFW exceeding 500 g. The overall correlation between clinical EFW and actual BW was weak (r = 0.4). There was a significant trend of improved accuracy of clinical EFW with increasing gestational age; however, BMI, fetal station, and admission diagnosis did not have significant effects. Of 221 cases of macrosomia (>4000 g), 181 (81.9%) were undetected by clinical EFW.

CONCLUSION

The correlation between clinical EFW and actual BW is overall weak, particularly in patients with macrosomic fetuses; however, BMI, admission diagnosis, and fetal station do not have a significant impact.

Fetal weight estimation: comparison of two-dimensional US and MR imaging assessments

PURPOSE

To prospectively define fetal density in the second half of pregnancy by using magnetic resonance (MR) imaging and to compare estimates of fetal weight based on ultrasonography (US) and MR imaging with actual birth weight.

MATERIALS AND METHODS

Written informed consent was obtained for this ethics committee-approved study. In this cross-sectional study between March 2011 and May 2012, fetal density was calculated as actual birth weight at delivery divided by fetal body volume at MR imaging in 188 fetuses between 20 weeks and 2 days and 42 weeks and 1 day of gestational age. Regression analysis was used to investigate the effect of variables, including sex, on fetal density. The US estimate of fetal weight was performed according to Hadlock et al, and the MR estimate of fetal weight was calculated based on the equation developed by Baker et al. US and MR estimates of fetal weight were compared with actual birth weights by using regression analysis.

RESULTS

Median fetal density was equal to 1.04 (range, 0.95-1.18). Fetal density was significantly associated with gestational age at delivery but not with fetal sex. In 26.6% of fetuses, the US estimate of fetal weight had a relative error of more than 10%, while a similar relative error for the MR estimate of fetal weight occurred in only 1.1% of fetuses. The limits of agreement were narrower with the MR estimate of fetal weight compared with the US estimate of fetal weight.

CONCLUSION

In the second half of pregnancy, fetal density varies with gestational age. Fetal weight estimates by using fetal MR imaging are better than those by using prenatal US.

How should bladder wall thickness be measured? A comparison of vaginal, perineal and abdominal ultrasound

INTRODUCTION

Measurement of bladder wall thickness using transvaginal ultrasound has previously been shown to discriminate between women with diagnosed detrusor overactivity and those with urodynamic stress incontinence. So far, no comparison has been made between abdominal, perineal and vaginal route for the measurement of bladder wall thickness. The aim of this prospective study was to determine if abdominal, perineal and vaginal ultrasound measurements of bladder wall thickness are comparable with each other.

METHODS

125 patients with lower urinary tract symptoms were asked to participate in the study. All patients had measurements at the trigone, the bladder dome and the anterior bladder wall. The order of either the abdominal, perineal or vaginal approach was computer-assisted randomly assigned. Ultrasound was performed using the Aloka SSD-1400 (Aloka® Co Ltd, Japan) with the vaginal 5 Mhz probe UST-984-5 and the abdominal and perineal probe was a 3.5Mhz curved array for SSd-1400. Ultrasound examination was made with the patient in supine position with a residual of less than 50ml.

RESULTS

Means of bladder wall thickness are significantly different (p<0.05). Vaginal measurement of bladder wall thickness showed the smallest values for bladder wall thickness, abdominal the largest. At the trigone, differences were significant between vaginal and perineal ultrasound but not between abdominal and perineal approach.

CONCLUSION

Bladder wall thickness measurements do differ depending on the vaginal, perineal or abdominal approach.

The effects of maternal weight gain patterns on term birth weight in African-American women

OBJECTIVE

The goals of our study were (1) to estimate the trends in maternal weight gain patterns and (2) to estimate the influence of variation in maternal weight and rate of weight gain over different time periods in gestation on variation in birth weight in African-American and non-African-American gravidas.

STUDY DESIGN AND SETTING

Data from a prospective cohort study in which pregnant women were monitored at multiple time points during pregnancy were analysed. Maternal weight was measured at three times during pregnancy: preconception (W(0)); 16-20 weeks gestation (W(1)); 30-36 weeks gestation (W(2)), in a cohort of 435 women with full-term singleton pregnancies. The relationship between gestational age-adjusted birth weight (aBW) and measures of maternal weight and rate of weight gain across pregnancy was estimated using a multivariable longitudinal regression analysis stratified on African-American race.

RESULTS

The aBW was significantly associated with maternal weight measured at any visit in both strata. For African-American women, variation in aBW was significantly associated with variation in the rate of maternal weight gain in the first half of pregnancy (W(01)) but not the rate of maternal weight gain in the second half of pregnancy (W(12)); while for non-African-American women, variation in aBW was significantly associated with W(12) but not W(01).

CONCLUSION

Factors influencing the relationship between aBW and maternal weight gain patterns depend on the context of the pregnancy defined by race. Clinical decisions and recommendations about maternal weight and weight gain during pregnancy may need to account for such heterogeneity.