Analysis of factors influencing the ultrasonic fetal weight estimation

Predicting the fetal weight by ultrasonography for isolated polyhydramnios: Comparison of 14 formulas

OBJECTIVE

To recalculate the estimated fetal weight (EFW) based on ultrasound measurements in patients complicated with isolated polyhydramnios, using 14 current formulas to observe which formula better predicts the EFW.

METHODS

This study examined pregnant women who gave birth in the hospital between January 2015 and January 2020. Maximum vertical pocket (MVP) was classified as, mild, moderate, and severe polyhydramnios, and the patients' measurements were reanalyzed using 14 formulas. The estimation of birth weight (EBW) alongside observed birth weight (OBW) facilitated the computation of statistical indices, namely the mean absolute percentage error (MAPE) expressed as [(EBW - OBW)/OBW × 100], the mean percentage error (MPE) denoted as (EBW - OBW)/(OBW × 100), and their corresponding 95% confidence intervals.

RESULTS

A total of 564 polyhydramnios patients were included in the study. When looking at the MAPE, the lowest rate (7.65) was found in the Hadlock 2 formula. Hadlock 1, Hadlock 3, and Shinozuka formulas demonstrated MAPE values most closely aligned with Hadlock 2. Weiner I and Thurnau were the formulas with the highest MAPE values. When the cut-off values for MAPE were taken as 10%, 4/14 of the formulas (Weiner I-II, Vintzleos and Thurnau) gave results above 10%. Among 14 formulas, 3 (21.4%) had positive (sonographic overestimation) (Hadlock 3, Shinozuka, and Vintzleos) and the other 11 (78.6%) had negative MPE (sonographic underestimation).

CONCLUSION

The Hadlock 2 formula had the lowest MAPE in predicting birth weight in patients with polyhydramnios, closely followed by the Hadlock 1, Hadlock 3, and Shinozuka formulas.

Performance of fetal ultrasound and magnetic resonance imaging in predicting birthweight according to the test-to-delivery interval: A cohort study

OBJECTIVE

To assess the influence of the test-to-delivery interval (TDI) on the performance of ultrasound (US) and magnetic resonance imaging (MRI) for predicting birthweight (BW).

STUDY DESIGN

This is a secondary analysis of a prospective, single center, blinded cohort study that compared MRI and US for the prediction of BW ≥ 95th percentile in singleton pregnancies. Patients that were included in the initial study underwent US and MRI for estimation of fetal weight between 36 + 0/7 and 36 + 6/7 weeks of gestation (WG). The primary outcome of the current study was to report the changes of US and MRI sensitivity and specificity in the prediction of BW > 95th percentile, BW > 90th percentile, BW < 10th percentile, and BW < 5th percentile, according to the TDI. The secondary outcome was to represent the performance of both tools in the prediction of BW > 90th percentile when TDI is<2 weeks, between 2 and 4 weeks, and>4 weeks. Receiver operating characteristic (ROC) curves were constructed accordingly.

RESULTS

2378 patients were eligible for final analysis. For the prediction of BW > 95th or 90th percentile, the sensitivity of MRI remains high until 2 weeks, and it decreases slowly between 2 and 4 weeks, in contrast to the sensitivity of US which decreases rapidly 2 weeks after examination (p < 0.001). For the prediction of BW < 10th or 5th percentile, the sensitivity of both tools decreases in parallel between 1 and 2 weeks. The specificities of both tools remain high from examination till delivery. These findings are reproducible with the use of the antenatal customized and the postnatal national growth charts.

CONCLUSION

The performance of MRI in the prediction of BW, especially in large-for-gestational age, is maximal when delivery occurs within two weeks of the examination, decreasing slightly thereafter, in contrast with the performance of US which decreases drastically over time.

Is accuracy of estimated fetal weight improved by better image quality scores?

OBJECTIVE

To assess in a group of ultrasound operators of various levels of experience the predictive value of systematic quality scoring to assess estimated fetal weight (EFW) validity.

METHODS

Screenshots, sonographer experience, and neonate birth weight were collected for 131 ultrasound examinations in the 7 days before birth. The difference (EFW error) between projected birth weight (EFW + [30 g × interval in days to birth]) and actual birth weight was then assessed (absolute value). Three senior sonographers rated all the screenshots (International Society of Ultrasound in Obstetrics and Gynecology 16-point score for image quality) and interobserver reproducibility was assessed concomitantly. The impact of the score on EFW accuracy was then assessed (univariate analysis). Receiver operating characteristic curves allowed us to assess the score's positive predictive value (PPV) for accurate EFW.

RESULTS

Mean birth weight was 2998 ± 954 g and mean EFW error was 8.6% ± 7.1%. Both the sonographer's experience and score significantly impacted the EFW error (P < 0.05). The PPVs of systematic image scores for identifying an EFW error greater than 10% and greater than 15% were appropriate for clinical use (areas under the curve 0.61 and 0.70, respectively). Score reproducibility was modest.

CONCLUSION

Low image scores and limited ultrasound expertise are associated with an increased risk of inaccurate EFW.

Impact of maternal body mass index on the accuracy of third trimester sonographic estimation of fetal weight

OBJECTIVES

To Determine whether maternal body mass index (BMI) can affect the accuracy of sonographic estimation of fetal weight (EFW) in the third trimester when compared to neonatal birthweight (BW).

METHODS

Secondary analysis from our original prospective cohort of pregnant women beyond 34 weeks, distributed in 4 groups according to their BMI: normal, overweight, obese and morbid obese. Fetal biometry and fluid measurements were obtained by two experienced sonographers, blinded for patient's clinical information and to each other's measurements. Average EFW and neonatal BW were converted into gestational-specific Z-scores. Interobserver correlation coefficient (ICC) and Cronbach's reliability coefficient (CRC) were calculated. Bland-Altman (BA) plots were constructed to assess the level of accuracy.

RESULTS

100 women were enrolled (800 measurements obtained by 17 sonographers): 17 had normal BMI (17%), 27 were overweight (27%), 29 were obese (29%) and 27 were morbidly obese (27%). There was no statistical difference for GA at delivery (p = 0.74), EFW (p = 0.05) or BW (p = 0.09) between groups (Table 1). Mean Z-score for EFW was - 0.17 (SD 0.81) and for neonatal BW was - 0.25 (SD 0.74). ICC was 0.69 (95% CI 0.57, 0.78) and CRC was 0.82. Mean Z-score difference was small (Table 2). When stratifying according to BMI categories, the ICC ranged from 0.49 to 0.76. Reliability indices ranged from 0.66 to 0.86. The Z-scores' differences were overall small with no statistical difference (Table 3). BA showed evenly distributed interobserver differences (Fig. 1).

CONCLUSIONS

When performed by trained sonographers, fetal weight estimation in the third trimester is accurate when compared to neonatal birthweight at increasing BMI categories.

The birth weight of macrosomia influence the accuracy of ultrasound estimation of fetal weight at term

OBJECTIVE

To evaluate and analyze the accuracy of ultrasound estimation of the fetal weight of Macrosomia at term.

METHOD

The instruments used were α6(Aloka; Japan) color Doppler ultrasound imagers, and vinno 80 (feieno; China) with a frequency of 3.5 MHz. The formula used to calculate the estimated fetal birth weight (EFW) was that proposed by Hadlock et al. (Hadlock 2). The biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) measurements were performed strictly following the practice guidelines. Detailed measurement standards are shown in the figure and the table in the text. Macrosomia is typically defined as a birth weight above the 90th percentile for gestational age or >4000 g.Two indexes were used to calculate the error between EFW and birth weight (BW): Simple error (SE = BW - EFW); Absolute percentage error (APE, which reflects this percentage in absolute value, percentage error [PE = SE/BW] × 100). In order to better evaluate the measurement results, we made the following definitions: 1. When APE > 15%, the measurement deviation is significant. 2. The ratio of those cases with APE > 15% to the total number of cases measured by a sonographer was greater than 20%, indicating that the sonographer was prone to significant measurement deviation.

RESULT

A total of 374 cases were analyzed. The mean maternal age was 31.48 (±15.93) years. Each pregnant woman carries only one fetus. The mean gestational age at delivery was 39.93 (±0.84) weeks. There were 245 male infants (65.5%), 129 female infants (34.5%), 214 cesarean section (57.2%), and 160 vaginal delivery (42.7%). 339 cases (90.64%) were estimated to be lower than the actual BW. The estimated weight was higher than the actual weight in 35 cases, accounting for 9.36%.The APE>15% in 56 cases, accounting for 14.97%. The accuracy of estimated fetal weight was closely related to the BW of the fetus and had no significant correlation with the seniority of the physician, the gender of the fetus, and the fetal position.

CONCLUSION

Studies on macrosomia have shown that the BW of macrosomia tends to be underestimated, which is also reflected in the results of this study. The accuracy of estimated fetal weight still needs to be improved. Our study found that the accuracy of estimated fetal weight was closely related to the BW of the fetus and had no significant correlation with the seniority of the physician, the gender of the fetus, and the fetal position. The correlation between the section and calculation formula on the measurement accuracy needs to be studied. Through systematic data analysis, we can find the doctors whose measurements are relatively inaccurate in our department and carry out targeted quality control to improve the measurement accuracy.

Accuracy of estimated fetal weight in extremely preterm infants and the impact of prepregnancy body mass index

BACKGROUND

Antenatally, we rely on ultrasound estimated fetal weight as a proxy for birthweight to inform discussions regarding perinatal morbidity and mortality. Maternal obesity may negatively impact the quality of ultrasound imaging, and thus, understanding the associations between obesity and estimated fetal weight in the preterm period is important.

OBJECTIVE

Given the rising obesity rates and association with preterm birth, we sought to determine the accuracy of ultrasound-derived estimated fetal weight in predicting birthweight in preterm infants by prepregnancy body mass index and to evaluate the accuracy of estimated fetal weight in predicting birthweight between small-for-gestational-age and appropriate-for-gestational-age infants.

STUDY DESIGN

We included all women who delivered a live-born singleton infant between 23 0/7 and 31 6/7 weeks of gestation and had an ultrasound estimated fetal weight within 7 days before delivery. We calculated the mean percentage difference between estimated fetal weight and birthweight and the absolute percent difference. Excess error was defined as an absolute percentage difference of >20%. We used multivariable modified Poisson models to determine the association between prepregnancy body mass index and small for gestational age and excess ultrasound error.

RESULTS

Our cohort included 641 infants with a mean gestational age of 28.0±2.6 weeks and a mean birthweight of 1110±425 g. More than one-third of our cohort were obese (227 [35%]). The mean percentage difference between estimated fetal weight and birthweight was 7.7%±11.2% among all infants. Ultrasound overestimated birthweight in 77% of the cohort (n=492). Stratified by body mass index, the mean percentage differences between estimated fetal weight and birthweight were 6.7%±11.0% in women with normal weight and 9.5%±12.0% in women with obesity (P=.02). The mean percentage differences between estimated fetal weight and birthweight were 11.0%±11.0% in small-for-gestational-age infants (n=80) and 7.1%±11.0% in appropriate-for-gestational-age infants (P<.001). Small-for-gestational-age infant was associated with an increased risk of excess ultrasound error with an adjusted relative risk of 2.3 (95% confidence interval, 1.2-4.3).

CONCLUSION

Although ultrasound estimated fetal weight overestimated birthweight, particularly in small-for-gestational-age infants, most estimates were within 10% of actual birthweight. Obesity and small-for-gestational-age birth were both associated with an increased risk of excess ultrasound error (≥20%) in estimating birthweight.

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.

Observer Influence with Other Variables on the Accuracy of Ultrasound Estimation of Fetal Weight at Term

Background and Objectives: The accuracy with which the estimation of fetal weight (EFW) at term is determined is useful in order to address obstetric complications, since it is a parameter that represents an important prognostic factor for perinatal and maternal morbidity and mortality. The aim of this study was to determine the role of the experienced observers with other variables that could influence the accuracy of the ultrasound used to calculate EFW at term, carried out within a period of seven days prior to delivery, in order to assess interobserver variability. Materials and Methods: A cross-sectional study was performed including 1144 pregnancies at term. The validity of the ultrasound used to calculate EFW at term was analyzed using simple error, absolute error, percentage error and absolute percentage error, as well as the percentage of predictions with an error less than 10 and 15% in relation to maternal, obstetric and ultrasound variables. Results: Valid predictions with an error less than 10 and 15% were 74.7 and 89.7% respectively, with such precision decreasing according to the observer as well as in extreme fetal weights. The remaining variables were not significant in ultrasound EFW at term. The simple error, absolute error, percentage error and absolute percentage error were greater in cases of extreme fetal weights, with a tendency to overestimate the low weights and underestimate the high weights. Conclusions: The accuracy of EFW with ultrasound carried out within seven days prior to birth is not affected by maternal or obstetric variables, or by the time interval between the ultrasound and delivery. However, accuracy was reduced by the observers and in extreme fetal weights.

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.

Analysis of factors influencing accuracy of ultrasound-based fetal weight estimation

Context:

The primary objective of this study was to examine the impact of maternal age, parity, gestational age, fetal gender, gestational diabetes mellitus, and pregnancy-induced hypertension on the accuracy of ultrasonography-based fetal weight estimation. The secondary objective was to find the impact of a formula selection on the accuracy of fetal weight estimation.

Subjects and Methods:

The inclusion criteria were a live-birth singleton pregnancy and the last ultrasound scan to delivery interval ≤7 days. Fetal weight was estimated using the Hadlock-4 formula. To study the concurrent impact of all the factors on the accuracy, cases were divided into two subcategories based on percentage error, with ±10% as a threshold. The accuracy of Hadlock-4 formula was compared with the two Indian population-based formulas, Hiwale-1 and Hiwale-2.

Results:

In total, 184 cases were included in the study. It was observed that the systematic error in weight estimation was significantly less in the male fetuses (8.45 ± 9.34%) in comparison to the female fetuses (11.71 ± 10.34%). The combined impact of all the factors on the accuracy was found to be nonsignificant by the multivariate analysis. The Hiwale-1 (-0.59 ± 8.75%) and Hiwale-2 (-0.65 ± 8.7%) formulas had statistically significant less errors compared to the Hadlock-4 formula (11.67 ± 7.95%).

Conclusion:

All the studied clinical factors were found to have a limited impact on the overall accuracy of fetal weight estimation. However, the formula selection was found to have a significant impact on the accuracy, with the native population-based formulas being significantly more accurate.

The effect of fetal weight on the accuracy of sonographic weight estimation among women with diabetes

Objective: The assessment of sonographic estimated fetal weight (EFW) enables identification of fetuses in the extremes of weight, thus aiding in the planning and management of peripartum care. There are conflicting reports regarding the accuracy of EFW in diabetic mothers. We aimed to study the factors associated with the accuracy of EFW at term, specifically the role of gestational and pre-gestational diabetes in this setting.Methods: A retrospective study including all women carrying singleton term gestations who delivered within a week following a sonographic fetal weight estimation between 2011 and 2019. Accurate EFW was defined as within 10% of the actual birthweight. We allocated the study cohort into two groups: (1) Accurate EFW (2) inaccurate EFW. Both groups were compared in order to identify factors associated with the inaccuracy of EFW.Results: Overall, 41,263 deliveries were available for evaluation, including 412 (1.0%) deliveries among women with pre-gestational diabetes and 4,735 (11.5%) among women with gestational diabetes. Of them, 7,280 (17.6%) had inaccurate EFW. Inaccurate EFW was associated with nulliparity, OR 0.82 [95% CI] (0.78-0.87), oligohydramnios, OR 0.81 [95% CI] (0.71-0.93), pregestational diabetes, OR [95% CI] 0.61 (0.50-0.79), and extremity of fetal weight; <2,500 grams-OR [95% CI] 0.37 (0.33-0.41) and >4,000 grams OR [95% CI] 0.52 (0.48-0.57). On multiple regression analysis, the following factors were independently associated with inaccurate EFW: pregestational diabetes, OR [95% CI] 0.58 (0.46-0.73), p < .001, nulliparity, OR [95% CI] 0.86 (0.82-0.91), p < .001 and higher fetal weight (for each 500 grams), OR [95% CI [1.25 (1.21-1.30), p < .001. On analysis of different weight categories, pregestational diabetes was associated with inaccurate EFW only in those with birthweight >3,500 grams, OR [95% CI] 0.37 (0.24-0.56) (p < .001).Conclusion: Among pregestational diabetic women, the accuracy of sonographic EFW when assessed to be >3,500 grams is questionable. This should be taken into consideration when consulting women and planning delivery management.Synopsis: Among pregestational diabetic women, the accuracy of estimated sonographic fetal weight higher than 3,500 grams is of limited accuracy.

False diagnosis of small for gestational age and macrosomia - clinical and sonographic predictors

Purpose: To investigate clinical and sonographic features associated with sonographic accuracy for the prediction of small for gestational age (SGA) and macrosomia at birth.Methods: The database of a tertiary medical center was retrospectively searched for women who gave birth at term to a singleton healthy neonate in 2007-2014 and underwent sonographic estimated fetal weight (sEFW) evaluation within 3 d before delivery. Fetal growth restriction (FGR) and SGA were defined as sEFW or birth weight <10th percentile for gestational age; macrosomia was defined as birth weight >4000 grams. Data on maternal age, parity, gestational age, fetal gender, presentation, placental location, diabetes, hypertension, and oligo/polyhydramnios were compared between pregnancies with a false-negative and false-positive diagnosis of SGA or macrosomia.Results: Of the 5425 fetal weight evaluations, 254 (4.7%) deviated by >15% from the actual birth weight. Nulliparity, absence of diabetes, neonatal female gender, anterior placenta, lower birth weight, and oligohydramnios were associated with a high deviation. We identified 482 SGA neonates (8.9%) and 633 macrosomic neonates (11.7%). A false-positive diagnosis of FGR was associated with oligohydramnios, absence of diabetes, and posterior placenta, and a false-negative diagnosis, with older maternal age, nulliparity, and male gender. A false-positive diagnosis of macrosomia was associated with older maternal age, multiparity, polyhydramnios, anterior placenta, and lack of hypertensive complications, and a false-negative diagnosis, with diabetes, hypertension, oligohydramnios, and vertex presentation.Conclusion: The accuracy of sEFW is affected by clinical and sonographic pregnancy characteristics. Further analyses should focus on improving accuracy especially at the fetal weight extremes.

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.

A modified model can improve the accuracy of foetal weight estimation by magnetic resonance imaging

PURPOSE

To determine whether birth weight can be reliably estimated using three-dimensional (3D) magnetic resonance imaging (MRI) foetal body volume at term.

METHOD

Foetuses between 37⁺⁵ weeks and 41 weeks of gestation were delivered within 7 days after MRI and ultrasound (US) examinations. 3D foetal models were reconstructed from MRI data, and body volume was calculated. The MRI-based weight estimations were calculated using the Baker equation and the modified Baker equation with a higher density coefficient. The US-based weight estimations were determined using the formula by Hadlock. Estimations based on MRI and US were compared with the birth weights.

RESULTS

Among 22 foetuses that underwent both US and MRI evaluations within 48 h before labour, the mean random errors for the estimated weight based on US, the Baker equation and the modified Baker equation were 6.5%, 4.8%, and 4.8%, respectively, and these methods correctly estimated the weights of 77.3%, 86.4% and 100% of the foetuses to within 10% of the actual birth weight. The weights of 95.5% of the foetuses were underestimated by the Baker equation. Similar findings were observed among 103 estimations based on both US and MRI within 7 days before delivery. The mean relative error of the MRI-determined estimate of foetal weight using the modified Baker equation was not significantly associated with foetal sex, birth weight, gestational age at MRI examination, the MRI-to-delivery interval or the type of MRI scanner.

CONCLUSION

A modified Baker equation with a high-density coefficient can improve the accuracy of foetal weight estimation based on 3D MRI foetal volume at term, and its accuracy was not significantly affected by foetal characteristics or the type of MRI scanner among births occurring within 7 days after examinations.

The accuracy of ultrasound estimation of fetal weight in comparison to birth weight: A systematic review

Ultrasound estimation of fetal weight is a highly influential factor in antenatal management, guiding both the timing and mode of delivery of a pregnancy. Although substantial research has investigated the most accurate ultrasound formula for calculating estimated fetal weight, current evidence indicates significant error levels. The aim of this systematic review was to identify the most accurate method, whilst identifying sources of inaccuracy in order to facilitate recommendations for future practice. Seven studies met the inclusion criteria and 11 different formulae were assessed; ultrasound calculation of fetal weight was most commonly overestimated. The Hadlock A formula produced the most accurate results, with the lowest levels of random error. Methods incorporating just two measurement parameters were inconsistent, producing large random errors across multiple studies. Key sources of inaccuracy included difficulties obtaining accurate fetal measurements in late gestation; the remainder were operator dependent, including lack of experience and insufficient training and audit. The accuracy of ultrasound estimated fetal weight has improved in the last decade, though a lack of consistency remains evident. National implementation of a rigorous audit programme would likely improve accuracy further, and increase the confidence and clinical value of the method.

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.

A new mathematical formula to predict the foetal weight in twin pregnancies: A comparison of it with 19 different formulas

One hundred and seventy-two twin-pregnant patients were enrolled. The estimated foetal weight was calculated using 19 different formulas. Ong's formula (0.954 (95%CI = 0.938/0.966)), which was designed specifically for twins, produced the highest Cronbach's alpha value followed by Hadlock II (0.952 (95%CI = 0.935/0.965)), Hadlock I (0.952 (95%CI = 0.935/0.964)), Hadlock III (0.952 (95%CI = 0.935/0.964)), Hadlock IV (0.952 (95%CI = 0.935/0.964)) and our formula (0.952 (95%CI = 0.935/0.964)), which produced the same Cronbach's alpha values for twin A. For twin B, our formula produced the highest Cronbach's alpha value (0.961 (95%CI = 0.948/0.972) followed by Hadlock II (0.960 (95%CI = 0.946/0.971)), Hadlock I (0.960 (95%CI = 0.946/0.970)), Hadlock III (0.960 (95%CI = 0.946/0.970)) and Hadlock IV (0.960 (95%CI = 0.946/0.970)). In conclusion, our formula (AC, FL) performed well in predicting the foetal weights in twin pregnancies (>24 weeks) in our study. However, it should be tested in other populations. Hadlock II (AC, FL) produced a comparable performance to Hadlock I (BPD, HC, AC, FL), Hadlock III (BPD, AC, FL) and Hadlock IV (HC, AC, FL). Hadlock II may be preferable in twin pregnancies since it is based on AC and FL only.

Comparison of Errors of 35 Weight Estimation Formulae in a Standard Collective

Issue: The estimation of foetal weight is an integral part of prenatal care and obstetric routine. In spite of its known susceptibility to errors in cases of underweight or overweight babies, important obstetric decisions depend on it. In the present contribution we have examined the accuracy and error distribution of 35 weight estimation formulae within the normal weight range of 2500-4000 g. The aim of the study was to identify the weight estimation formulae with the best possible correspondence to the requirements of clinical routine. Materials and Methods: 35 clinically established weight estimation formulae were analysed in 3416 foetuses with weights between 2500 and 4000 g. For this we determined and compared the mean percentage error (MPE), the mean absolute percentage error (MAPE), and the proportions of estimates within the error ranges of 5, 10, 20 and 30 %. In addition, separate regression lines were calculated for the relationship between estimated and actual birth weights for the weight range 2500-4000 g. The formulae were thus examined for possible inhomogeneities. Results: The lowest MPE were achieved with the Hadlock III and V formulae (0.8 %, STW 9.2 % or, respectively, -0.8 %, STW 10.0 %). The lowest absolute error (6.6 %) as well as the most favourable frequency distribution in cases below 5 % and 10 % error (43.9 and 77.5) were seen for the Halaska formula. In graphic representations of the regression lines, 16 formulae revealed a weight overestimation in the lower weight range and an underestimation in the upper range. 14 formulae gave underestimations and merely 5 gave overestimations over the entire tested weight range. Conclusion: The majority of the tested formulae gave underestimations of the actual birth weight over the entire weight range or at least in the upper weight range. This result supports the current strategy of a two-stage weight estimation in which a formula is first chosen after a pre-estimation of the weight range.

Update Reference Charts: Fetal Biometry between the 15th and 20th Week of Gestation

OBJECTIVE

The aim of this study was to derive reference charts between the 15th and 20th week of gestation for biparietal diameter (BPD), occipito-frontal diameter (OFD), head circumference (HC), abdominal circumference (AC) and femur length (FL) compared to commonly used curves and to evaluate the impact of maternal body mass index (BMI), ultrasound equipment, fetal gender and nicotine abuse.

METHODS

In a cross-sectional study of 4,265 low-risk pregnancies, biometric data were obtained between the 15th and 20th week of gestation. The statistical analysis included descriptive data, fitting regression curves for the 5th, 50th and 95th quantile as well as multivariate quantile regression analyses.

RESULTS

Reference curves for BPD, OFD, HC, AC and FL showed a linear increase between the 15th and 20th week of gestation. New equations and reference charts are presented in this study. In a comparison of influence factors sex, BMI and ultrasound systems have an impact.

CONCLUSION

As a result of the study, we determined current growth curves for BPD, OFD, HC, AC and FL for both sexes as well as for males and females separately. The updated growth curves for all biometric parameters differ from the curves used commonly in the last two decades.

Intrapartum sonographic weight estimation

PURPOSE

To evaluate the accuracy of intrapartum sonographic weight estimation (WE).

MATERIALS AND METHODS

This retrospective, cross-sectional study included 1958 singleton pregnancies. Inclusion criteria were singleton pregnancy with cephalic presentation, vaginal delivery and ultrasound examination with complete biometric parameters performed on the day of delivery during the latent or active phase of labor, and absence of chromosomal or structural anomalies. The accuracy of intrapartum WE was compared to a control group of fetuses delivered by primary cesarean section at our perinatal center and an ultrasound examination with complete biometric parameters performed within 3 days before delivery (n = 392). Otherwise, the same inclusion criteria as in the study group were applied. The accuracy of WE was compared between five commonly applied formulas using means of percentage errors (MPE), medians of absolute percentage errors (MAPE), and proportions of estimates within 10 % of actual birth weight.

RESULTS

In the whole study group, all equations showed a systematic underestimation of fetal weight (negative MPEs). Overall, best MAPE and MPE values were found with the Hadlock II formula, using BPD, AC and FL as biometric parameters (Hadlock II, MPE: -1.28; MAPE: 6.52). MPEs differed significantly between WE in the study and control group for all evaluated formulas: in the control group, either no systematic error (Hadlock III, IV and V) or a significant overestimation (Hadlock I, II) was found. Regarding MAPEs, application of the Hadlock III (HC, AC, FL) and V (AC) formula resulted in significant lower values in the control group (Hadlock III, MAPE: 7.48 vs. 5.95, p = 0.0008 and Hadlock V, MAPE: 8.79 vs. 7.52, p = 0.0085). No significant differences were found for the other equations.

CONCLUSIONS

A systematic underestimation of fetal weight has to be taken into account in sonographic WE performed intrapartum. Overall, the best results can be achieved with WE formulas using the BPD as the only head measurement.

Obesity and the challenges of ultrasound fetal abnormality diagnosis

Prenatal ultrasound has become an essential clinical tool for aneuploidy screening, detection of fetal congenital anomalies, and assessment of fetal growth and well-being. Maternal obesity, an increasing global problem, has been shown to decrease the accuracy of ultrasound examination in high-risk pregnancy. The purpose of this review is to provide an evidenced-based perspective on the challenges of performing fetal ultrasound in obese women and to provide a practical guide on how to care for these patients in the ultrasound suite.

A search for the most accurate formula for sonographic weight estimation by fetal sex - a retrospective cohort study

OBJECTIVE

The aim of this study was to assess the effect of fetal sex on the accuracy of multiple formulas for sonographic estimation fetal weight (SEFW).

METHODS

The cohort included all singleton live births recorded at a single medical center from January 2004 to September 2011. The accuracy of SEFW was compared between male and female fetuses using 6575 SEFW performed within 3 days prior to delivery. Fetal weight was estimated using 27 models.

RESULTS

The accuracy of different formulas in predicting birth weight of male and female fetuses was found to be significantly different in almost every accuracy index that was compared (P < 0.05). The model by Sabbagha et al. was found to be the most accurate in assessing female fetuses. The most accurate model for male fetuses was a sex-specific formula by Melamed et al. We also found that a combination of the most accurate formula for each sex to one combined sex-specific model increased SEFW accuracy significantly.

CONCLUSION

The accuracy of SEFW is significantly related to fetal sex. The combination of the formulas by Melamed et al. and Sabbagha et al. for male and female fetuses accordingly allowed more accurate SEFW in our research population.

Factors influencing the accuracy of fetal weight estimation with a focus on preterm birth at the limit of viability: a systematic literature review

BACKGROUND

Fetal weight estimation (FWE) is an important factor for clinical management decisions, especially in imminent preterm birth at the limit of viability between 23(0/7) and 26(0/7) weeks of gestation. It is crucial to detect and eliminate factors that have a negative impact on the accuracy of FWE.

DATA SOURCES

In this systematic literature review, we investigated 14 factors that may influence the accuracy of FWE, in particular in preterm neonates born at the limit of viability.

RESULTS

We found that gestational age, maternal body mass index, amniotic fluid index and ruptured membranes, presentation of the fetus, location of the placenta and the presence of multiple fetuses do not seem to have an impact on FWE accuracy. The influence of the examiner's grade of experience and that of fetal gender were discussed controversially. Fetal weight, time interval between estimation and delivery and the use of different formulas seem to have an evident effect on FWE accuracy. No results were obtained on the impact of active labor.

DISCUSSION

This review reveals that only few studies investigated factors possibly influencing the accuracy of FWE in preterm neonates at the limit of viability. Further research in this specific age group on potential confounding factors is needed.

The influence of maternal body mass index on fetal weight estimation in twin pregnancy

OBJECTIVE

Sonographic estimated fetal weight (EFW) is important in the management of high-risk pregnancies. The possibility that increased maternal body mass index (BMI) adversely affects EFW assessments in twin pregnancies is controversial. The aim of this study was to investigate the effect of maternal BMI on the accuracy of EFW assessments in twin gestations prospectively recruited for the ESPRiT (Evaluation of Sonographic Predictors of Restricted growth in Twins) study.

STUDY DESIGN

One thousand one twin pair pregnancies were recruited. After exclusion, BMI, birthweights, and ultrasound determination of EFW (within 2 weeks of delivery) were available for 943 twin pairs. The accuracy of EFW determination was defined as the difference between EFW and actual birthweight for either twin (absolute difference and percent difference). Cells with less than 5% of the population were combined for analysis resulting in the following 3 maternal categories: (1) normal/underweight, (2) overweight, and (3) obese/extremely obese.

RESULTS

Analysis of the 3 categories revealed mean absolute variation values of 184 g (8.0%) in the normal/underweight group (n = 531), 196 g (8.5%) in the overweight group (n = 278), and 206 g (8.6%) in the obese/extremely obese group (n = 134) (P = .028, which was nonsignificant after adjustment for multiple testing). Regression analysis showed no linear or log-linear relationship between BMI and the accuracy of EFW (P value for absolute difference = .11, P value for percentage difference = .27).

CONCLUSION

Contrary to a commonly held clinical impression, increasing maternal BMI has no significant impact on the accuracy of EFW in twin pregnancy.

The accuracy of ultrasound-estimated fetal weight in extremely preterm infants: a comparison of small for gestational age and appropriate for gestational age

OBJECTIVES

To compare the accuracy of estimated fetal weight (EFW) in extremely preterm small for gestational age (SGA) and appropriate for gestational age (AGA) infants and report other significant factors influencing the accuracy of EFW.

METHODS

A retrospective cohort study of singleton pregnancies 22(+0) -27(+6)  weeks. Women were included in the study if an ultrasound scan had been performed within seven days of delivery, with no major fetal anomaly and data available to calculate customised birthweight (BW) centiles. Mean error of EFW and actual BW and mean % error of EFW and actual birthweight were compared for SGA and AGA infants. A stepwise backward elimination linear regression model was used to determine the significant factors influencing the accuracy of EFW.

RESULTS

A total of 134 cases (51 SGA and 83 AGA) were analysed. The mean gestational age at delivery was 25(+2)  weeks (SD 11.5 days) and mean BW 711 g (SD 227 g). Overall mean percentage error of EFW and actual BW was 8.8% (range 0-34.6%). There was a significant difference in mean error of EFW and actual BW for SGA and AGA deliveries (mean +16 g versus -23 g, respectively, P = 0.01) and in mean % error of EFW (11.2%, 95%CI 9.1-13.3 versus 7.4%, 95% CI 6.2-8.6 P = 0.009). Factors that significantly influenced the accuracy of EFW included SGA (P = 0.001, coeff. = -3.73, 95% CI -5.94/-1.52), scan to delivery interval (P = 0.02, coeff. = 0.66, 95% CI 0.12/1.21) and reduced amniotic fluid (P = 0.008, coeff = 3.61, 95% CI -5.47/-0.85).

CONCLUSIONS

Ultrasonographic EFW for extreme preterm SGA fetuses is less accurate than AGA fetuses and is more likely to overestimate EFW. This should be considered when counselling women with growth restricted fetuses at the limits of viability.

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.

Fetal sex and intrauterine growth patterns

OBJECTIVES

To analyze the effect of fetal sex on intrauterine growth patterns during the second and third trimesters.

METHODS

We conducted a cross-sectional study of women with uncomplicated singleton pregnancies who underwent sonographic fetal weight estimation during the second and third trimesters in a single tertiary center. The effect of fetal sex on intrauterine growth patterns was analyzed for each of the routine fetal biometric indices (biparietal diameter, head circumference, occipitofrontal diameter, abdominal circumference, and femur length) and their ratios. Sex-specific regression models were generated for these indices and their ratios as a function of gestational age. Sex-specific growth curves were generated from these models for each of the biometric indices and their ratios for gestational weeks 15 to 42.

RESULTS

Overall, 12,132 sonographic fetal weight estimations were included in the study. Fetal sex had an independent effect on the relationship between each of the biometric indices and their ratios and gestational age. These effects were most pronounced for biparietal diameter (male/female ratio, 1.021) and the head circumference/femur length and biparietal diameter/femur length ratios (male/female ratios, 1.014 and 1.016, respectively). For the head measurements, these sex-related differences were observed as soon as the early second trimester, whereas for abdominal circumference, the differences were most notable during the late second and late third trimesters.

CONCLUSIONS

Female fetuses grow considerably slower than male fetuses, and these differences are observed from early gestation. However, the female fetus is not merely a smaller version of the male fetus, but, rather, there is a sex-specific growth pattern for each of the individual fetal biometric indices. These findings provide support for the use of sex-specific sonographic models for fetal weight estimation as well as the use of sex-specific reference growth charts.

Sonographic weight estimation in fetuses with breech presentation

PURPOSE

To assess the accuracy of weight estimation (WE) in fetuses with breech presentation and to compare it directly with a control group of fetuses in vertex presentation.

MATERIALS AND METHODS

In a retrospective cohort study, the accuracy of WE in fetuses with breech presentation (n = 244) was evaluated using eight sonographic models and was compared with a control group of fetuses in vertex presentation (n = 244). Each fetus underwent ultrasound examination with complete biometric parameters within 7 days before delivery. The accuracy of the different formulas was compared using means of percentage error (MPE), a measure that reflects systematic error; standard deviation values of MPEs, a measure for random error; medians of absolute percentage error (MAPE), which take both the systematic and random error into account and the percentage of fetal WEs falling within a 10 % range of the actual birth weight.

RESULTS

Significantly lower (more negative) MPE values were found in the breech group with the Hadlock (AC, FL) formula, whereas no significant differences were seen with any of the other equations. When compared to zero, in the breech group, a significant systematic error was found with five formulas, while in the control group a significant systematic error was found with three equations. With regard to random error and MAPE, no significant differences were found between the two groups, irrespective of the formula applied. Generally, in both groups, formulas based on three or four biometric indices were more accurate in detecting fetal weight than formulas with only one or two parameters.

CONCLUSIONS

Weight estimation in fetuses with breech presentation was as accurate as weight estimation in fetuses with vertex presentation. Using the currently available, well-established formulas should therefore also be appropriate for WE in fetuses with such malpresentations.

Accuracy of sonographic fetal weight estimation: a matter of presentation

OBJECTIVES

To assess the accuracy of sonographic weight estimation for fetuses in breech presentation, and to determine whether certain sonographic models perform better than others in cases of breech presentation.

METHODS

This was a retrospective cohort study of all sonographic weight estimations of fetuses in breech presentation performed within 3 days prior to delivery (n = 165). The accuracy of weight estimation was evaluated using eight sonographic models and was compared with a control group of fetuses in vertex presentation matched to the study group by birth weight and fetal gender (n = 165).

RESULTS

After exclusion of a model based on femur diaphysis length alone, which was found to be highly inaccurate, the systematic error for fetuses in breech presentation was smaller than that observed for fetuses in vertex presentation (mean of all models - 0.14% vs. 2.0%, P = 0.01). The random error was higher in cases of breech presentation (9.4-13.2% vs. 7.5-8.9%, P < 0.05), and was lower for models that are based on three to four biometric indices (9.4-9.5%) compared with models that incorporate one to two biometric indices (10.8-13.6%, P < 0.05). Overall, the higher random error outweighed the decrease in the systematic error, as reflected by the lower fraction of weight estimations within 10% of birth weight among fetuses in breech presentation. Models based on three to four biometric indices were more accurate in detecting the weight thresholds beyond which a trial of vaginal delivery is usually not recommended.

CONCLUSION

Sonographic weight estimation appears to be less accurate for fetuses in breech presentation, principally because of a larger random error. The use of sonographic models that are based on three to four biometric indices, training aimed at improving measurement in breech fetuses and the development of sonographic models derived from fetuses in breech presentation, may improve the accuracy of weight estimation in these cases.

Accuracy of sonographic weight estimation as a function of fetal sex

OBJECTIVES

To determine whether the accuracy of sonographic fetal weight estimation is related to fetal sex.

METHODS

The accuracy of sonographic fetal weight estimation was compared between male and female fetuses using 3672 sonographic weight estimations performed within 3 days prior to delivery. Fetal weight was estimated using eight regression models that are based on different combinations of the following biometric parameters: abdominal circumference (AC), femur diaphysis length (FL), biparietal diameter (BPD) and head circumference (HC).

RESULTS

In seven out of the eight models tested, the presence of a male fetus was associated with a significantly lower systematic error compared with a female fetus (-0.2 to 2.1% vs. 1.3 to 6%, P<0.001). On multivariate analysis, fetal sex was independently associated with sonographic accuracy so that the likelihood of a weight estimation within 10% of birth weight was 30% higher for male fetuses compared with female fetuses. The biometric parameters that contributed most to these sex-related differences were FL and AC, while models that included HC were associated with the lowest differences in the systematic error between male fetuses and female fetuses. For most models, the random error and correlation between estimated weight and birth weight were not affected by fetal sex (8.1-12.8% vs. 8.2-13.6%, and 0.856-0.944 vs. 0.842-0.944, respectively).

CONCLUSION

Sonographic estimation of fetal weight is more accurate for male fetuses than for female fetuses. The use of sex-specific models may improve the accuracy of fetal weight estimation for female fetuses.

Factors affecting the accuracy of ultrasonographical fetal weight estimation in twin pregnancies

OBJECTIVE

To determine the factors affecting the accuracy of ultrasonographic weight estimation in twins.

METHODS

152 sets of twins delivered vaginally, were included. Effects of fetal weights, inter-twin weight discordance, chorionicity, early rupture of membranes, intrauterine growth restriction, and presentations of twins on errors of estimated fetal weights were evaluated. The primary measures of estimated fetal weight accuracy compared were mean-percentage-error and the standart deviation (SD) of percentage errors.

RESULTS

Mean percentage errors for the first fetus (8.13 ± 6.82) and the second fetus (8.07 ± 6.88) were similar (p = 0.64). Random errors of both fetuses were also similar (p = 0.78). If one of the fetuses had IUGR, the percentage error and also the random error of that fetus would increase significantly. Different presentations and fetal gender combinations were similar for both types of errors of fetal weight estimation. A weak negative lineer relationship was found between the weight of the first fetus and its percentage error (r = -0.27, p = 0.04). A similar relation was present between the weight and percentage error of the second fetus (r = -0.29, p = 0.03). Percentage errors and also random errors of both fetuses were significantly higher if severe discordance was present between twins (p = 0.01 and p = 0.02, respectively).

CONCLUSIONS

IUGR, fetal weights, and inter-twin discordence are the factors affecting the accuracy of weight estimation by ultrasonography.

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.