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.     

Accuracy of sonographic estimation of fetal weight before induction of labor in diabetic pregnancies and pregnancies with suspected fetal macrosomia

AIMS: To evaluate the accuracy of sonographic estimation of fetal weight (EFW) in diabetic pregnancies and pregnancies with suspected fetal macrosomia. METHODS: 63 women with diabetic pregnancies, 74 nondiabetic women with suspected large-for-gestational-age (LGA) infants, and 161 controls underwent ultrasound assessment prior to induction of labor. EFW was compared to the weight at birth, 1-3 days later. RESULTS: EFW was highly correlated to birth weight. Absolute or actual weight differences between the birth weight and the EFW, and the rate of EFW within 10% of birth weight were not different between the groups. A linear regression model controlling for maternal and gestational age, diagnosis of gestational or pregestational diabetes, birth weight, gravidity, parity, nulliparity, placental location and AFI was not significantly correlated to the absolute or actual weight differences. In pregnancies with suspected LGA, higher birth weight was an independent and significant predictor of high weight difference inaccuracy. CONCLUSIONS: The ultrasonographic EFW 1-3 days before delivery is highly correlated with birth weight, reaffirming the clinical use of abdominal circumference and femur length in estimating fetal weight near labor at term. In pregnancies with suspected LGA fetuses and higher prevalence of macrosomia, ultrasound has higher sensitivity but lower specificity than the controls.     

Accuracy of ultrasonography fetal weight estimation in twin pregnancies

ObjectivesUltrasonography is an essential tool in the management of twin pregnancies. Fetal weight estimation is useful to anticipate neonatal care in case of prematurity, growth restriction or growth discordance. The aim of this study was to evaluate the accuracy of ultrasound fetal weight prediction in twin pregnancies.Patients and methodsTwo hundred and twenty-four patients with an ultrasonography within 7 days before birth were retrospectively studied. Estimated fetal weight (EFW) was calculated with the Hadlock's formula and was compared with birth weight (BW). Growth restriction and growth discordance superior or equal to 25% between the first (T1) and the second twin (T2) were recorded.ResultsAbsolute differences between EFW and BW were similar for both twins (127 g [56.25–210] for T1 and 110 g [50–206.25] for T2). Mean absolute percentage error was 5.41% (2.32–9.65) for T1 and 5.64% (2.46–10.37) for T2 and was superior to 10% for 24% of T1 and 27% of T2. Gestational age inferior to 32 weeks, obesity and oligoamnios were associated with a better accuracy of ultrasonography. Chorionicity as well as fetal presentation did not influence fetal weight estimation. Ultrasonography in the diagnosis of growth restriction had a sensitivity of 82%, a specificity of 76%, a positive predictive value (PPV) of 22% and a negative predictive value (NPV) of 98%. For diagnosis of growth discordance, sensitivity was 72%, specificity 95%, PPV 72% and NPV 95%.ConclusionFetal weight can be accurately predicted in twin pregnancies. The contribution of ultrasonography in the diagnosis of growth restriction and growth discordance is mainly due to a high NPV.     

Accuracy of ultrasonographic fetal weight estimation in twin pregnancies

OBJECTIVE: To compare the accuracy of fetal weight estimations between normal and growth-restricted twin and singleton pregnancies in a single tertiary center. METHODS: The computerized ultrasound database of a tertiary center was searched for all fetal weight estimations made in twin pregnancies from 2001 to 2006, which were performed up to 3 days before delivery. Accuracy was compared with a control group of singleton pregnancies at a 3:1 ratio. Estimated fetal weight was calculated by the Hadlock formula. Analyses were performed for the whole group and for pregnancies associated with fetal growth restriction and discordancy. RESULTS: The study groups included 278 twins and 834 singleton pregnancies. The twins group was characterized by a higher mean absolute percentage error compared with the singleton group (8.9% compared with 6.8%). Accuracy was lower for the second twins than for the first twins. When comparing the subgroup of fetal growth restriction, differences in sensitivity and specificity were small for singleton compared with overall twins (47.5% compared with 48.9% and 97.7% compared with 95.7%, respectively). Overall accuracy was better in the singleton group (95% compared with 88%), mainly due to relatively low accuracy in the second twin (86%). For detection of discordancy, estimated fetal weight had a sensitivity of 52%, specificity of 88%, and overall accuracy of 81%. CONCLUSION: The accuracy of the ultrasonographic estimated fetal weight seems to be lower for twin gestations than for singleton gestations, especially for second twins. These data should be considered by clinicians when making decisions based on ultrasonographic characteristics.     

Sonographic fetal weight estimation in a south-east Asian population.

OBJECTIVES: To determine the optimal sonographic fetal weight estimation formula for a mixed south-east Asian population near term. METHODS: Seventy-eight uncomplicated pregnancies were monitored between January 1996 and January 1997. Biparietal diameter, head circumference, abdominal circumference and femur length were measured and the following formulae were tested: Campbell, Shepherds and Hadlock. The estimated fetal weight was calculated by 12 different methods. The weight estimate was then projected forward to the time of delivery using the gestation-adjusted forward projection method. The weight estimation error was derived from the difference between the projected fetal weight and birth weight, and expressed as a percentage of birth weight. RESULTS: The mean time interval from the time of ultrasound fetal weight estimation to delivery was 4.4 days. The birth weight ranged between 2,330 to 4,215 g. The best performing formula was Hadlock's formula using the head circumference, abdominal circumference and femur, with the perimeters calculated using the ellipse function. The standard deviation of error for this formula was 8.66%. CONCLUSION: Even though the Hadlock formula was originally derived from an American population, it was equally useful in south-east Asian population.     

Reliability of sonographic fetal weight estimation in triplet pregnancies: a retrospective cohort study

Purpose

To review our experience in ultrasound fetal weight estimation in our large population of triplet pregnancies.

Methods

Ninety-seven triplet pregnancies were retrospectively included between January 2003 and January 2017. Sonographic fetal weight estimation using Hadlock’s and Schild’s formulas was compared to actual birth weight in a tertiary-care center in Vienna, Austria. Statistical analyses were performed using a stepwise linear regression model and crosstabs.

Results

The median discrepancy between the sonographically estimated fetal weight by Hadlock’s formula and the actual birth weight was 106 g (IQR 56–190). The percentage error and its standard deviation were ??2.5?±?12.1%, and the median percentage error was ??3.6%. Concerning the use of Hadlock’s formula, estimated fetal weight was the most important factor predictive of actual birth weight with an estimate of 0.920 (p?<?0.001). Female neonates had been overestimated by a mean of 50.473 g per fetus. The sonographic prediction of small-for-gestational-age neonates was significantly reliable (p?<?0.001), with positive and negative predictive values ranging from 81.3 to 100.0%. Similar results were obtained for Schild’s formula.

Conclusion

Even if sonographically estimated fetal weight in triplet pregnancies has a high overall accuracy of fetal weight estimation, there are some limitations in prediction of intrauterine growth restrictions, especially in female fetuses.

     

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.     

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 ultrasonic fetal weight estimation and detection of small for gestational age fetuses

One hundred and eight-six pregnant women were studied with ultrasound for clinical suspicion of poor fetal growth. Fetal weight was estimated using biparietal diameter and mean abdominal diameter with a special nomogram. The fetal femur length (FL) to abdominal circumference (AC) ratio was also calculated. The mean interval between the last ultrasound examination and delivery was 9 days (range, 0 to 14 days). Eighty-three women had their last ultrasonic examination 0 to 4 days (mean, 2 days) before delivery. In this group the arithmetic mean of weight estimation errors was -1 gm (SD, 159 gm). The signed mean percent error was +0.6% (SD, 6.6%). Neither systematic nor random errors were found between different growth percentile groups. When small for gestational age (SGA) was defined as birthweight below 2.5 percentile, the sensitivity, specificity, and positive predictive value of the weight estimations were 82%, 92%, and 84%, respectively, in 186 cases. Significant differences were found in FL to AC ratios between growth pattern groups but fetal weight estimation was found to be superior in the detection of SGA fetuses.     

Diagnosis of macrosomia in the postdates population: combining sonographic estimates of fetal weight with glucose challenge testing

OBJECTIVE: To evaluate the test characteristics of sonographic estimation of fetal weight in the detection of macrosomia in nondiabetic postdates patients as a function of maternal glucose value measured after glucose challenge testing performed at 24-28 weeks of gestation. METHODS: At or beyond 41 weeks' gestation, 656 nondiabetic patients had sonographic estimation of fetal weight. Receiver-operator characteristic curve analysis was used to define the glucose value at which an optimal number of macrosomic fetuses could be identified. The test characteristics of sonography in the prediction of macrosomia in the two populations defined by that cut-off value were evaluated. RESULTS: A glucose level of 120 mg/dL (6.6 mM) was identified as the optimal cutoff for prediction of birth weight > or = 4,000 g. In the group with a glucose level > or = 120 mg/dL, sonographic estimation of fetal weight in the detection of macrosomia offered a sensitivity, specificity, and positive and negative predictive values of 63%, 91%, 71%, and 86%, respectively. In those with glucose level <120 mg/dL, sonography demonstrated a sensitivity, specificity, and positive and negative predictive values of 65%, 89%, 60%, and 91%, respectively. CONCLUSIONS: In postdates nondiabetic patients, routine glucose challenge testing performed early in pregnancy has limited ability to improve the test characteristics of sonography to predict macrosomia. The positive predictive value of sonographically suspected macrosomia increases from 60-71% in patients whose glucose level was > or = 120 mg/dL (P = 0.002).     

A comparison of sonographic estimation of fetal weight and obstetrically determined gestational age in the prediction of neonatal outcome for the very low-birth weight fetus

A comparison of sonographic estimation of fetal weight and obstetrically determined gestational age in the prediction of neonatal outcome for the very low-birth weight fetus was conducted in a study population of 122 fetuses. With stepwise logistic regression, obstetric gestational age was found to be the best predictor of neonatal death, while sonographic estimated fetal weight did not add significantly to this prediction. However, both variables were important in the prediction of adverse neonatal outcome (neonatal death together with major neonatal complications of prematurity.