Ultrasonic estimation of fetal weight at term: an evaluation of eight formulae

AIM: To compare the accuracy of eight sonographic formulae for predicting fetal birth weight at term in a multiethnic population. METHODS: Pregnant women at term who were booked for induction of labor or elective cesarean section were included in the study. Eight ultrasonic fetal biometric formulae were used to predict fetal birth weight. RESULTS: A total of 173 patients were included in the study; 53 (30.6%) patients were from the Indian subcontinent, 44 (25.4%) patients were from Africa, 33 (19.1%) patients were from the Arabian Peninsula and 43 (24.9%) were from other ethnic groups. The mean absolute error ranged from a minimum of 0.3% (+/-11.3) for Hadlock (biparietal diameter [BPD], head circumference [HC], abdominal circumference [AC], femur length [FL]) to a maximum of 37.5% (+/-10.0) for Warsof (FL). The correlation of estimated fetal weight with actual birth weight ranged from a minimum of 0.09 with Warsof (FL) to a maximum of 0.77 with Shepard and Warsof (BPD, AC) and Hadlock (BPD, HC, AC, FL). The combination of AC with BPD measurements rather than FL achieves a high level of accuracy. CONCLUSIONS: Shepard (BPD, AC) provides a simple and accurate logarithm for the prediction of fetal weight at term in the studied multiethnic population.     

The effect of maternal hemoglobin concentration on fetal birth weight according to trimesters

Objective: To investigate the relationship between fetal birth weight and maternal hemoglobin concentrations in different trimesters.

Methods: This prospective cross-sectional study comprised 329 women, monitored and delivered between January 2013 and January 2014 in our clinic. Hemoglobin concentrations in all trimesters and all birth weights of the newborns were recorded. Comparisons and correlations were made of the maternal hemoglobin concentrations and birth weights in each trimester.

Results: A positive correlation was determined between fetal weight and increased first trimester maternal hemoglobin concentration (p: 0.025). No correlation was found between fetal weights and second and third trimester hemoglobin concentrations (p?=?0.287, p?=?0.298, respectively). When the effect of independent factors on fetal weight was investigated, it was determined that birth week and first trimester hemoglobin levels were the factors of most influence.

Conclusions: Low hemoglobin concentrations in the first trimester of gestation seem to be associated with low fetal birth weights. Anemia can directly cause poor in utero fetal growth due to inadequate oxygen flow to the placental tissue or it can be an indirect indicator of maternal nutrition deficiency. In both circumstances, this study reveals that treatment of anemia before and in the early stages of pregnancy is directly correlated with better fetal outcomes.     

Fetal biometry and fetal weight estimation: JSUM standardization

From the clinical point of view, it is very important to standardize methods of fetal growth evaluation. The standardization committee of fetal measurement of the Japanese Society of Ultrasound in Medicine (JSUM) announced the recommended standard procedure for fetal biometry, calculation of estimated fetal weight (EFW) and their evaluation method. In short, the abdominal circumference (AC) by the ellipse-tracing method should be the standard for the fetal abdominal measurement and the EFW should be calculated by the following formula:

EFW = 1.07 × BPD. + 0.30 × AC × FL,

where BPD is the biparietal diameter and FL the femur length.     

Clinical and sonographic estimation of fetal weight performed during labor by residents

OBJECTIVE: This study was undertaken to assess the accuracy of both clinical and sonographic estimations of the fetal weight (EFW) performed during the active phase of labor by residents. METHODS: The study protocol consisted of achieving clinical, followed by sonographic EFW by the admitting resident during the active phase of labor. Patients who had an EFW (clinical or sonographic) within the last 2 weeks were excluded from the study. In addition, the effect of the following variables on the accuracy of the EFW were examined: maternal age, maternal weight and body mass index, parity, the Bishop score before obtaining the EFW, gestational age, birth weight, and the postgraduate year of the examiner. The Pearson correlation, chi2 test, and Student t test were the statistical analyses used. We also calculated the sensitivity, specificity, and positive and negative predictive values for clinical and sonographic EFW for detecting macrosomia (birth weight > or = 4000 g). RESULTS: A total of 192 patients participated in this study. The coefficient of correlation between the clinical and sonographic EFW and the actual birth weight was 0.59 (P < .0001) and 0.65 (P < .0001), respectively. Clinical EFW was correct (within +/-10%) in 72% of the cases and the sonographic EFW was correct (within +/-10%) in 74% of the cases. However, the sensitivity of predicting birth weight of 4 kg or more was only 50% for both clinical and sonographic EFW, with 95% and 97% specificity, respectively. None of the clinical variables that were tested were significantly associated with the accuracy of the EFW. CONCLUSION: Both clinical and sonographic EFW performed during the active phase of labor by residents correlate with the actual birth weight but have poor sensitivity in detecting macrosomic fetuses. Sonographic EFWs offer no advantage over clinical EFWs.     

Accuracy of fetal weight estimation by ultrasound in periviable deliveries

Abstract

Objective: To evaluate the accuracy of ultrasound estimated fetal weight (EFW) near viability, and to determine the adequacy of use of EFW in place of birth weight (BWT) for predicting prognosis for infants born near the limit of viability.

Methods: Retrospective chart review of women delivering between 22^0/7 and 25^6/7 weeks gestation (GA) with ultrasound performed within 7 days of delivery. Potentially relevant clinical factors were evaluated regarding their impact on accuracy of EFW. Estimated survival based on BWT and EFW, using an National Institute for Child Health and Human Development (NICHD) algorithm, were compared.

Results: Study included 93 infants. Mean absolute percent difference (accuracy) of EFW for BWT was 9.4% (95%CI 7.4–11.3). There was no correlation between EFW accuracy and BWT, GA, maternal age, or BMI. There was a 3% overestimation of BWT per 100?g decrease in BWT (p?=?0.001). Race, oligohydramnios, parity, smoking, or previous cesarean did not impact EFW accuracy. Mean predicted survival by the NICHD algorithm was 43.1% using BWT; 43.6% using EFW (p?=?0.63). An overestimation of predicted survival (using EFW instead of BWT) greater than 20% was detected in only two cases.

Conclusion: Accuracy is similar to prior studies. Estimated newborn survival based on EFW is similar to that based on BWT.     

Divergence of estimated fetal weight and birth weight in singleton fetuses

Objective: To evaluate differences in distribution of estimated fetal weight (EFW) and birth weight (BW) of ongoing fetuses and neonates of the same gestational age.

Methods: Reference curves for EFW (Hadlock BPD-HC-AC-FL formula, N?=?1191) and BW (N?=?1036) in singleton pregnancies from 24⁺⁰ to 40⁺⁶ gestational weeks were calculated. Multiple pregnancies, fetuses with major or multiple abnormalities or syndromes and iatrogenic preterm deliveries due to preeclampsia or abnormal fetal Doppler were excluded. The standardized residuals for EFW and BW were calculated and compared.

Results: EFW and BW can be accurately described by quadratic equations (R²?=?0.944 and 0.807, respectively). The distribution of standardized residuals for BW using the EFW formula was negative from 28⁺⁰ to 35⁺⁶ weeks. The 50th and 5th centiles of BW were lower than those of EFW throughout prematurity, and they converged at approximately 38 gestational weeks. The 5th centile for BW was 30% lower than the 5th centile for EFW at 27 weeks, 27.5% lower at 30 weeks and 19.4% at 34 weeks.

Conclusions: Preterm infants have lower BW distribution compared to the expected EFW of ongoing pregnancies of the same gestational age, supporting the concept of hidden intrauterine morbidity for a proportion of these infants.     

Comparison of the accuracy of INTERGROWTH-21 formula with other ultrasound formulae in fetal weight estimation

Objective

A new ultrasound formula for fetal weight estimation was proposed from the INTERGROWTH-21 project in 2017. There is no comparison of its accuracy with other ultrasound formulae. This study aims to compare the accuracy of INTERGROWTH-21 formula in fetal weight estimation with the traditional Hadlock1 and Shepard formula.

Accuracy of sonographic fetal weight estimation of fetuses with a birth weight of 1500 g or less

Objective

To compare 35 commonly used formulae for small and average sized fetuses on their accuracy in estimating the birth weight in fetuses of 1500 g or less.

Study design

For this retrospective study a database search was performed for all singleton pregnancies without structural or chromosomal defects and with a birth weight of 1500 g or less where the last ultrasound examination was performed within seven days before delivery. Percentage error and absolute percentage error were calculated based on 35 different weight estimation formulae. Multiple regression analysis was used to determine the significant contributors to the absolute percentage error.

Results

One hundred and ninety-three cases fulfilled the inclusion criteria. The median birth weight was 990 g. The percentage error ranged between −15.2% (underestimation with the Merz I formula) and 37.4% (overestimation with the Jordaan formula) and the respective standard deviations between 10.5% (Mielke I) and 54.0% (Schillinger), respectively. The absolute percentage error was between 8.5% and 37.6%. The most accurate weight estimation was achieved with the formula from Mielke (percentage error 1.8% and absolute percentage error 8.5%). Multiple regression analysis showed that significant contributors to the percentage error of the Mielke formula were biparietal diameter (OR = −0.206, p = 0.045), occipitofrontal diameter (OR = 0.765, p < 0.0001), abdominal circumference (OR = −2.953, p < 0.0001), femur length (OR = −0.903, p < 0.0001), head to abdomen ratio (OR = −1.080, p < 0.0001) and fetal weight (OR = 2.847, p < 0.0001).

Conclusion

When estimating fetal weight in fetuses weighing 1500 g or less, one has to be aware of the great differences in accuracy among the formulae.     

Comparison of magnetic resonance imaging to ultrasound in the estimation of birth weight at term

OBJECTIVE: This study was undertaken to compare magnetic resonance (MR) and ultrasound (US) fetal weight estimates obtained immediately before delivery with birth weight. STUDY DESIGN: Eighty women scheduled for a cesarean delivery underwent a fast acquisition MR and US for fetal weight estimation within 3 hours of delivery. Prospective MR calculation was based on the equation 0.12+1.031 g/mLxfetal volume (mL)=MR weight (g). US fetal weight estimation was calculated by the formula by Hadlock et al. Estimations were compared with birth weight. RESULTS: Correlation (95% CI) between birth weight and MR weight is 0.95 with a mean absolute error of 129 g (105-155) compared with the correlation between birth weight and US of 0.85 with a mean absolute error of 225 g (186-264). The correlation for birth weight and MR imaging is significantly greater than that of birth weight and US, P<.001. CONCLUSION: Birth weight estimation is more accurate by MR imaging than by US in term infants.     

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 use of three-dimensional ultrasound does not improve training in fetal biometric measurements

Objective.?To investigate whether three-dimensional (3D) technology offers any advantage over two-dimensional (2D) ultrasound in fetal biometric measurement training.

Methods.?Ten midwives with no hands-on experience in ultrasound were randomized to receive training on 2D or 3D ultrasound fetal biometry assessment. Midwives were taught how to obtain fetal biometric measurements (biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL)) by a trainer. Subsequently, each midwife measured the parameters on another 10 fetuses. The same set of measurements was repeated by the trainer. The percentage deviation between the midwives' and the trainer's measurements was determined and compared between training groups. Time required for completion was recorded. Frozen images were reviewed by another sonographer to assess the image quality using a standardized scoring system.

Results.?The median time for the complete set of measurements was significantly shorter in the 2D than in 3D group (13.4?min versus 17.8?min, P?=?0.03). The mean percentage deviations did not reach statistical significance between the two groups except for FL (3.83% in 2D group versus 2.23% in 3D group (P?=?0.046)). There were no significant differences in the quality scores.

Conclusions.?This study showed that the only demonstrable advantage of 3D ultrasound was a slightly more accurate measurement of FL, at the expense of a significantly longer time required.     

Longitudinal ultrasound assessment of fetal presentation: a review of 1010 consecutive cases

BACKGROUND: Abnormal presentation (detected in the early third trimester) causes concern for pregnant women and their carers. Definitive ultrasound-based data on the risk of persistence of abnormal presentation is lacking to allow appropriate counselling. Comparison of pregnancy outcome was made on the basis of maternal age at delivery. METHODS: Notes of 1010 women (426 primigravidae, 584 multigravidae), with singleton pregnancies, confined between 1997 and 2005 were reviewed to extract: (i) the gestation based on 18-20-week ultrasound in conjunction with the patient's recorded last menstrual period, and (ii) the presentation of each antenatal visit from 28+ weeks until delivery. Previous obstetric history, maternal age, mode of delivery, birthweight and outcomes were also documented. RESULTS: At 28-30 weeks, 216 babies presented abnormally. By 38+ weeks, 54 persisted as either a breech or a transverse lie. Thus, an abnormal presentation in the early trimester carries a 22.2% chance of persisting at term. Continuance of abnormal presentation at each subsequent week of the third trimester increased the risk of a Caesarean delivery at term. Conversely, in only six cases, a cephalic presentation at 28-30 weeks converted to a breech or other presentation during the third trimester-- a risk of 0.75%. CONCLUSION: These statistics provide a useful tool in advising women of the chances of abnormal presentation at term based on the presentation at various stages of the third trimester, and prepare them for the potential requirement of a Caesarean section.     

Clinical estimation of fetal weight and the Hawthorne effect

Objective

The Hawthorne effect refers to improvement in performance solely due to the subject's knowledge that he or she is being studied. We sought to determine if an obstetrician's clinical estimation of fetal weight (EFW) is influenced by the Hawthorne effect seen in some clinical trials.

Study design

We compared obstetricians’ clinical EFW's obtained during a study period to those obtained prior to the study period in one institution. We included any patient presenting at ≥37 weeks gestation. We excluded multiple pregnancies and patients with a recent sonographic EFW.

Results

There was no difference in regards to the proportion of EFW's within 10% of the birthweight (67.9% vs. 68.5%, p = .91), the mean absolute difference of EFW-birthweight (282 ± 227 g vs. 285 ± 232 g, p = .88), or the mean absolute percent error (8.5 ± 7.4% vs. 8.6 ± 7.2%, p = .96). We also could not find any Hawthorne effect when we excluded resident physicians’ EFW's and when we analyzed the subgroup of newborns with a birth weight ≥4000 g.

Conclusion

An obstetrician's knowledge that he or she is being studied is unlikely to improve clinical EFW accuracy. Published clinical EFW accuracies are likely to be similar to those obtained in clinical practice.     

B型超声测量胎儿股骨皮下组织厚度预测胎儿体重

目的探讨应用Ｂ型超声测量胎儿股骨皮下组织厚度预测胎儿出生体重的临床价值。方法应用Ｂ型超声对１７８例胎儿的双顶径、头围、腹围、股骨长、股骨皮下组织厚度进行测量并与新生儿出生体重的关系进行分析。结果股骨皮下组织厚度与新生儿出生体重相关性最好（ｒ＝０．８６０１）,对巨大儿诊断的敏感性为９１％,特异性为９４％,胎儿股骨皮下组织厚度与孕周呈正相关（ｒ＝０．７０７０）。结论应用Ｂ型超声测量胎儿股骨皮下组织厚度预测胎儿出生体重,方法简单、准确,有较好的临床应用价值。     

Comparison of abdominal palpation, Johnson’s technique and ultrasound in the estimation of fetal weight in Northern Iran

Objectives

to assess the accuracy of abdominal palpation, Johnson's technique and ultrasound in the estimation of fetal weight (EFW).

Design, setting and participants

174 pregnant women were recruited at random in a large teaching hospital in Iran. Fetal weight was estimated by palpation and Johnson's technique at the time of admission by one qualified midwife, and then estimated by ultrasound by one radiologist. After birth, all newborns were weighed using the same scale.

Findings

a significant correlation was found between EFW by ultrasound, palpation and Johnson's technique and actual birth weight. The differences between EFW by palpation, ultrasound and Johnson's technique and actual birth weight were significant for small-for-gestational-age fetuses (p<0.05, p<0.01 and p<0.001, respectively), but not for appropriate-for-gestational-age fetuses. These differences were significant for ultrasound (p<0.001) and palpation (p<0.05) in large-for-gestational-age fetuses. The sensitivity of ultrasound for EFW of low-birthweight fetuses (72.2%) and the sensitivity of Johnson's technique for EFW of normal-weight and macrosomic fetuses (97.3% and 75%, respectively) appeared to be higher than the sensitivities of the other methods.

Conclusion

palpation and Johnson's technique can be used as alternatives to ultrasound for EFW, particularly if the measurements are taken by experienced, skilled personnel.     

Effect of second trimester and third trimester weight gain on immediate outcomes in neonates born to mothers with gestational diabetes: a retrospective observational study from India

Abstract

Aim: To evaluate the effect of second trimester and third trimester rate of weight gain on immediate outcomes in neonates born to mothers with Gestational Diabetes Mellitus (GDM).

Method and material: This retrospective observational study enrolled 593 eligible mothers. The records of all pregnant women booked before 24?weeks and screened for diabetes were eligible if they were diagnosed with Gestational Diabetes Mellitus (GDM) anytime during pregnancy. All the necessary maternal and neonatal details were collected from hospital database. The rate of weight gain was calculated at 18–24?weeks, 28–30?weeks, and that before delivery. The enrolled women were categorized into: poor weight gain, normal weight gain, and increased weight.

Results and discussion: The mean birth weight, length, and head circumference of neonates were significantly lower in women who had poor rate of weight gain in comparison with normal weight gain group. The mean prepregnancy BMI was significantly high in women with increased rate of weight gain when compared to normal weight gain women in second and third trimester. Regression analysis done to evaluate the independent effect of weight gain on C section and neonatal complications, showed that the independent predictors for cesarean section were previous cesarean section or 12.5 (95% CI 6.7–23) and conception by assisted reproductive technologies or 1.75 (95% CI 1.01–4.3), and the neonatal complications were influenced by birth weight or 1.5 (95% CI 1.1–2.2) and weight gain during second trimester or 1.26 (95% CI 1–1.6).

Conclusion: In women with GDM, reduced weight gain during pregnancy is associated with small for gestational age neonates. Caesarean section is predicted by previous C-section, and mode of conception whereas neonatal complications were predicted by birth weight and maternal weight gain during second trimester.     

Influence of fetal fat on the ultrasound estimation of fetal weight in diabetic mothers.

Currently available formulas for the estimation of fetal weight assume uniform density of tissue. Because fat tissue is less dense than lean body mass, we hypothesized that the sonographic overestimation of fetal weight in infants of diabetic mothers is the consequence of an elevated proportion of body fat, resulting in a lower body density. We prospectively examined 52 children of diabetic mothers. Each had ultrasound estimation of fetal weight within 7 days of delivery and estimates of neonatal body composition made from anthropometric evaluation within 48 hours of birth. Ultrasound estimates of fetal weight were considered acceptable if they were within 10% of actual birth weight. There was no difference in mean birth weight between those overestimated (N = 22) and those underestimated (N = 8). The sum of skinfolds from two sites, the ponderal index, and percent body fat were all significantly greater in the neonates with sonographic overestimation of fetal weight. Lean body mass was significantly greater (P less than .05) in infants whose sonograms underestimated birth weight. When all subjects were included, a significant correlation was found between the degree of error in the ultrasound estimation of fetal weight and the ponderal index (r = 0.40, P less than .01), the sum of the skinfold measurements (r = 0.29, P less than .05), and the present body fat (r = 0.28, P less than .05). These data suggest that increased body fat in infants of diabetic mothers is associated with sonographic overestimation of fetal weight.