Estimation of fetal weight before and after amniotomy in the laboring gravid woman

Comparison of sonographic fetal weight estimation formulas in patients with preterm premature rupture of membranes

BACKGROUND

Estimation of fetal weight (EFW) by ultrasound is useful in clinical decision-making. Numerous formulas for EFW have been published but have not been validated in pregnancies complicated by preterm premature rupture of membranes (PPROM). The purpose of this study is to compare the accuracy of EFW formulas in patients with PPROM, and to further evaluate the performance of the most commonly used formula - Hadlock IV.

METHODS

A retrospective cohort study of women with singleton gestations and PPROM, admitted to a single tertiary center between 2005 and 2017 from 22^0/7-33^0/7 (n = 565). All women had an EFW within 14 days of delivery by standard biometry (biparietal diameter, head circumference, abdominal circumference and femur length). The accuracy of previously published 21 estimated EFW formulas was assessed by comparing the Pearson correlation with actual birth weight, and calculating the random error, systematic error, proportion of estimates within 10% of birth weight, and Euclidean distance.

RESULTS

The mean gestational was 26.8 ± 2.4 weeks at admission, and 28.2 ± 2.6 weeks at delivery. Most formulas were strongly correlated with actual birth weight (r > 0.9 for 19/21 formulas). Mean systematic error was - 4.30% and mean random error was 14.5%. The highest performing formula, by the highest proportion of estimates and lowest Euclidean distance was Ott (1986), which uses abdominal and head circumferences, and femur length. However, there were minimal difference with all of the first 10 ranking formulas. The Pearson correlation coefficient for the Hadlock IV formula was strong at r = 0.935 (p < 0.001), with 319 (56.5%) of measurements falling within 10%, 408 (72.2%) within 15% and 455 (80.5%) within 20% of actual birth weight. This correlation was unaffected by gender (r = 0.936 for males, r = 0.932 for females, p < 0.001 for both) or by amniotic fluid level (r = 0.935 for mean vertical pocket < 2 cm, r = 0.943 for mean vertical pocket ≥2 cm, p < 0.001 for both).

CONCLUSIONS

In women with singleton gestation and PPROM, the Ott (1986) formula for EFW was the most accurate, yet all of the top ten ranking formulas performed quite well. The commonly used Hadlock IV performed quite similarly to Ott's formula, and is acceptable to use in this specific setting.

Comparison of the Hadlock and INTERGROWTH formulas for calculating estimated fetal weight in a preterm population in France

BACKGROUND

Accurate estimation of fetal weight is needed for growth monitoring and decision-making in obstetrics; the INTERGROWTH project developed an estimated fetal weight formula to construct new intrauterine growth standards.

OBJECTIVE

We sought to compare the accuracy of the Hadlock and INTERGROWTH formulas for the estimation of fetal weight among preterm infants.

STUDY DESIGN

Using the EPIPAGE 2 population-based study of births between 22-34 weeks of gestation, we included 578 nonanomalous singleton fetuses with an ultrasound-to-delivery interval <2 days. We used abdominal circumference, head circumference, and femur length to calculate estimated fetal weight with Hadlock formula and abdominal and head circumferences to calculate estimated fetal weight according to INTERGROWTH. The mean percentage errors and the proportions of estimated fetal weight measures within ±10% of birthweight were compared between the 2 methods.

RESULTS

Mean (SD) gestational age and birthweight were 29.1 (SD 2.7) weeks and 1219 (SD 489) g. Mean (SD) percentage errors for Hadlock and INTERGROWTH were significantly different: -0.7 (SD 10.1) and -3.5 (SD 11.6), respectively (P < .001), and more infants were classified within ±10% of their birthweight with Hadlock compared to INTERGROWTH (68.7% vs 57.8%, P < .001). The INTERGROWTH formula overestimated birthweight at 22-23 weeks compared to Hadlock [mean errors of 18.8 (SD 13.6) vs 5.5 (SD 10.2)] and underestimated birthweight >28 weeks: at 29-31 weeks, mean errors were -5.8 (SD 10.9) for INTERGROWTH and -0.6 (SD 10.4) for Hadlock.

CONCLUSION

Hadlock estimated fetal weight formula was more accurate than INTERGROWTH formula for fetuses delivered between 22-34 weeks of gestation. Our results support continued use of Hadlock formula in France and raise questions about the applicability of INTERGROWTH intrauterine growth standards.

Estimation of fetal weight by ultrasonography after preterm premature rupture of membranes: comparison of different formulas

OBJECTIVE

To compare different ultrasonographic fetal weight estimation formulas in predicting the fetal birth weight of preterm premature rupture of membrane (PPROM) fetuses.

METHODS

Based on the ultrasonographic measurements, the estimated fetal weight (EFW) was calculated according to the published formulas. The comparisons used estimated birth weight (EBW) and observed birth weight (OBW) to calculate the mean absolute percentage error [(EBW-OBW)/OBW×100], mean percentage error [(EBW-OBW)/OBW×100)] and their 95% confidence intervals.

RESULTS

There were 234 PPROM patients in the study period. The mean gestational age at which PPROM occured was 31.2±3.7 weeks and the mean gestational age of delivery was 32.4±3.2 weeks. The mean birth weight was 1892±610 g. The median absolute percentage error for 33 formulas was 11.7%. 87.9% and 21.2% of the formulas yielded inaccurate results when the cut-off values for median absolute percentage error were 10% and 15%, respectively. The Vintzileos' formula was the only method which had less than or equal to 10% absolute percentage error in all age and weight groups.

CONCLUSIONS

For PPROM patients, most of the formulas designed for sonographic fetal weight estimation had acceptable performance. The Vintzileos' method was the only formula having less than 10% absolute percentage error in all gestational age and weight groups; therefore, it may be the preferred method in this cohort. Amniotic fluid index (AFI) before delivery had no impact on the performance of the formulas in terms of mean percentage errors.

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.

Ultrasound Fetal Weight Estimation: How Accurate Are We Now Under Emergency Conditions?

The primary aim of this study was to evaluate the accuracy of sonographic estimation of fetal weight when performed at due date by first-line sonographers. This was a prospective study including 500 singleton pregnancies. Ultrasound examinations were performed by residents on delivery day. Estimated fetal weights (EFWs) were calculated and compared with the corresponding birth weights. The median absolute difference between EFW and birth weight was 200 g (100-330). This difference was within ±10% in 75.2% of the cases. The median absolute percentage error was 5.53% (2.70%-10.03%). Linear regression analysis revealed a good correlation between EFW and birth weight (r = 0.79, p < 0.0001). According to Bland-Altman analysis, bias was -85.06 g (95% limits of agreement: -663.33 to 494.21). In conclusion, EFWs calculated by residents were as accurate as those calculated by experienced sonographers. Nevertheless, predictive performance remains limited, with a low sensitivity in the diagnosis of macrosomia.

Sonographic fetal weight estimation - is there more to it than just fetal measurements?

OBJECTIVES

The primary aim of this study was to evaluate the effects of different maternal, fetal, and examiner related factors on the accuracy of sonographic fetal weight estimation (SFWE).

METHODS

A retrospective cohort study analyzing 9064 SFWEs performed within 1 week prior to delivery, including singleton pregnancies with a gestational age of 37 to 42 weeks, was recorded at one medical center from January 2004 to September 2011. Predicted birth weights were calculated according to models by Sabbagha et al., Hadlock et al., and Combs et al. and were compared with the actual birth weight. Effects of different factors on SFWE accuracy were assessed. The systematic error, random error, and mean absolute percentage error were used as measures of accuracy.

RESULTS

High maternal weight, height, body mass index, multiparity, older maternal age, diabetes, and fetal male sex were associated with underestimation of SFWE (P < 0.05). Fetal presentation and the sonographer's experience influenced SFWE differently using various models. The amniotic fluid index did have a significant effect on SFWE. Overall, more than 90% of the systematic errors were unaccounted for in the factors we assessed.

CONCLUSIONS

Many maternal and fetal factors significantly influence the SFWE; nevertheless, most errors are probably due to inherent problems in SFWE formulas.

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.

Sonographic prediction of macrosomia cannot be improved by combination with pregnancy-specific characteristics

OBJECTIVE

To evaluate the predictive value of a combination of sonographic, clinical and demographic data for detecting fetal macrosomia compared to ultrasound fetal weight estimation alone.

METHODS

Retrospective cohort data were obtained from 1062 pregnancies in an unselected population. Estimated fetal sonographic weight was obtained within the last week prior to delivery. Two different combination models-published by Mazouni et al. and Nahum and Stanislaw-were employed to predict the presence of macrosomia at birth in these infants. Receiver-operating characteristics (ROC) curves were generated to compare the prediction of macrosomia when using different observation methods and sensitivity, specificity, positive predictive value, negative predictive value (NPV) and accuracy were calculated.

RESULTS

Macrosomia (birth weight >or= 4000 g) was present in 135/1062 (12.7%) newborns. ROC curve analysis revealed the prediction of macrosomia using ultrasound alone to be significantly superior to the combined method of Mazouni et al. (area under the curve (AUC) 0.922, 95% CI 0.902-0.943 vs. 0.747, 95% CI 0.700-0.794, respectively; P < 0.0005), whereas the performance of the Nahum and Stanislaw equation was similar but not superior to ultrasound alone (AUC 0.895, 95% CI 0.839-0.950 vs. 0.912, 95% CI 0.867-0.958, respectively; P > 0.05). The accuracy of macrosomia prediction was similar for ultrasound alone and the Nahum and Stanislaw equation (approximately 90%), whereas the nomogram of Mazouni et al. reached only 51.7% accuracy (using a probability cut-off level of 50%). The NPV was found to be over 90% for all methods.

CONCLUSIONS

Combination of sonographic estimates with clinical and demographic variables does not improve the prediction of macrosomia at delivery in comparison with a routine ultrasound scan within a week before delivery, at least in unselected populations.

Analysis of factors influencing the ultrasonic fetal weight estimation

OBJECTIVE

The aim of our study was the evaluation of sonographic fetal weight estimation taking into consideration 9 of the most important factors of influence on the precision of the estimation.

METHODS

We analyzed 820 singleton pregnancies from 22 to 42 weeks of gestational age. We evaluated 9 different factors that potentially influence the precision of sonographic weight estimation (time interval between estimation and delivery, experts vs. less experienced investigator, fetal gender, gestational age, fetal weight, maternal BMI, amniotic fluid index, presentation of the fetus, location of the placenta). Finally, we compared the results of the fetal weight estimation of the fetuses with poor scanning conditions to those presenting good scanning conditions.

RESULTS

Of the 9 evaluated factors that may influence accuracy of fetal weight estimation, only a short interval between sonographic weight estimation and delivery (0-7 vs. 8-14 days) had a statistically significant impact.

CONCLUSION

Of all known factors of influence, only a time interval of more than 7 days between estimation and delivery had a negative impact on the estimation.

Clinical and ultrasound estimation of birth weight prior to induction of labor at term

OBJECTIVES

To assess and compare the accuracy of clinical and sonographic fetal weight estimation in predicting birth weight prior to induction of labor.

METHODS

In a prospective study of 262 women immediately prior to induction of labor, the fetal weight was estimated clinically by both the doctor (DR EFW) and the woman herself (WM EFW). A transabdominal scan was then performed to estimate the fetal weight sonographically using two different formulae-Shepard (SHEP EFW) and Hadlock (HAD EFW). The four estimated fetal weights were compared with the actual birth weight.

RESULTS

The mean percentage error was - 1.9 +/- 9.3% for DR EFW, - 3.4 +/- 12.6% for WM EFW, - 2.3 +/- 11.6% for SHEP EFW and - 7.6 +/- 10.6% for HAD EFW. All four EFWs were significantly different from birth weight (t = - 4.7, - 5.5, - 3.5 and - 11.4, respectively, all P < 0.01). The corresponding proportion of the EFWs which were within 10% of birth weight were 71%, 59%, 62% and 42%, respectively. The sensitivity and specificity of detecting a fetus weighing < 3000 g were 56% and 98% for DR EFW, 90% and 89% for WM EFW, 93% and 83% for SHEP EFW and 100% and 76% for HAD EFW. The corresponding values for detecting a fetus weighing > 4000 g were 16% and 99%, 29% and 96%, 48% and 92% and 40% and 94%, respectively.

CONCLUSIONS

Although, in general, clinical estimates of birth weight perform favorably compared with ultrasonographic estimates, ultrasound immediately prior to labor is more accurate at predicting the low- or high-birth-weight fetus.

[Accuracy of ultrasonic fetal weight estimation using head and abdominal circumference and femur length]

INTRODUCTION

Former investigations have shown that the accuracy of fetal weight estimation is significantly higher if several ultrasonic fetal parameters are measured, because the total body mass depends on the size of fetal head, abdominal circumference and femur length. The aim of this investigation was to establish the best regression model, that is a number of combinations of fetal parameters providing the most accurate fetal weight estimation in utero in our population.

MATERIAL AND METHODS

This prospective study was carried out at the Gynecology and Obstetrics Clinic of the Clinical Center Novi Sad. It included 270 pregnant women with singleton pregnancies within 72 hours of delivery who underwent ultrasound measurements of the biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL).

RESULTS

In regard to fetal weight estimation formulas, the deviation was lowest using regression models that simultaneously analyzed four fetal parameters (0. 55%) with SD +/- 7.61%. In these models the estimates of fetal weights were within +/- 5% of actual birth weight in 48.89%, and within +/- 10% of actual birth weight in 81.48%. Good results were also obtained using AC, FL measurements (0.92% +/- 8.20) as well as using AC, HC, FL measurements (-1.45% +/- 7.81). In our sample the combination of AC and FL model gave better results in fetal weight estimation (0.92 +/- 8.20%) than the one using BPD and AC (2.97 +/- 8.83%). Furthermore, the model using parameters AC, HC and FL showed a lower error in accuracy (-1.45 +/- 7.81%) than the model using BPD, AC and FL (2.51 +/- 7.82%).

CONCLUSION

This investigation has confirmed that the accuracy of fetal weight estimation increases with the number of measured ultrasonic fetal parameters. In our population the greatest accuracy was obtained using BPD, HC, AC and FL model. In cases when fast estimation of fetal weight is needed, AC, HC, FL model may be appropriate, but if fetal head circumference cannot be measured (amnion rupture and/or fetal head already in the pelvis) the AC, FL model should be used.

A systematic review of the ultrasound estimation of fetal weight

OBJECTIVES

The range and use of ultrasound fetal measurements have gradually been extended. Measurements have been combined to estimate fetal weight by mathematically based non-linear regression analysis or physically based volumetric methods. Fetal weight estimation is inaccurate, with poor sensitivity for prediction of fetal compromise. Several authors have shown the unacceptable level of intra- and interobserver variability in fetal measurement and the impact of errors on growth assessment. The aims of this study were to review the available methods and possible sources of inaccuracy.

METHODS

Four databases were searched for studies comparing ultrasound estimated fetal weight (EFW) with birth weight. Studies meeting the inclusion criteria evaluated 11 different methods. Errors were graphically summarized.

RESULTS

No consistently superior method has emerged. Volumetric methods provide some theoretical advantages. Random errors are large and must be reduced if clinical errors are to be avoided.

CONCLUSIONS

The accuracy of EFW is compromised by large intra- and interobserver variability. Efforts must be made to minimize this variability if EFW is to be clinically useful. This may be achieved through averaging of multiple measurements, improvements in image quality, uniform calibration of equipment, careful design and refinement of measurement methods, acknowledgment that there is a long learning curve, and regular audit of measurement quality. Further work to improve the universal validity and accuracy of fetal weight estimation formulae is also required.

Ultrasonographic estimation of fetal weight: acquiring accuracy in residency

OBJECTIVE

Ultrasonographic imaging is considered an objective means for fetal weight estimation. The goals of this study were to determine the accuracy of ultrasonographic estimates of fetal'weight performed by residents in training and to ascertain how rapidly the residents gained proficiency in this regard.

METHODS

A total of 300 ultrasonographic estimates of fetal weight and corresponding birth weight were collected and stratified into 4 groups by the level of residents' experience, from level 1 (inexperienced, with <6 months of exposure) to level 4 (advanced experience, with at least 24 months of training). The proportional difference between ultrasonographic estimates of fetal weight and birth weight was calculated for each case and grouped according to the level of training of the examiner. The derived data were compared by analysis of variance, linear regression, and chi2 test.

RESULTS

Significant increases in the accuracy of ultrasonographic estimates of fetal weight were observed with advancing levels of resident experience (P< .0001). Overall, 30.6% of ultrasonographic estimates of fetal weight fell within 5% of birth weight, and 60.6% fell within 10%. Among the least experienced residents (<6 months of training), 49.4% of estimates fell within 10% of birth weight; among those with 6 to 11 months of experience, 53.5% of estimates fell within 10%; among those with 12 to 23 months of experience, 64.1 % of estimates fell within 10%; and among the most experienced (>24 months), 73.6% of estimates fell within 10%.

CONCLUSIONS

There is a learning curve for ultrasonographic estimates of fetal weight, with a significant decrease in the percent error seen with advancing training among residents, reaching acceptable levels of more than 70% of estimates within 10% of birth weight after 24 months of ultrasonographic experience.